Baby Steps Toward Quantum Computers

Mz6 writes "In a step toward making ultra-powerful computers, scientists have transferred physical characteristics between atoms by using a phenomenon called entanglement, which Einstein derided as 'spooky action at a distance' before experiments showed it was real. Such 'quantum teleportation' of characteristics had been demonstrated before between beams of light. Teleportation between atoms could someday lie at the heart of powerful quantum computers, which are probably at least a decade away from development. Researchers using lab techniques can create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle." Reader starannihilator adds: "Physics Web provides a good graphic summary of the phenomenon, as well as a good technical article."

Comments

Buy stock now!!

[Anonymous Coward]

Be sure to invest in Skynet while the gittin's good.

Re:Buy stock now!!

[Rhodey]

It's -1 Troll because no one around here has the first fucking clue about how to moderate.

Analogue vs Digital

[Nermal6693]

I think (although I'm not certain) I read somewhere that a quantum computer is like an analogue computer - where you're not restricted by 0 and 1. Is that correct?

Re:Analogue vs Digital

[Anonymous Coward]

It was just a dream, Bender. There's no such thing as two.

Re:Analogue vs Digital

[LnxAddct]

A quantum computer is completely different. The only thing in common in the binary number system. In a classical computer you have bits, either a 1 or a 0. In quantum computers you have qubits which can be a 1 or a 0 or actaully both values at the same time! This can manifest tself in amazing ways. You can try every solution to a problem instantaneously because instead of having to count throught all of the possible inputs, i.e. going from 0 to 255 with 8 classical bits, in a quantum computer 8 qubits actualy are the values of 0 through 255 all at the same time. The answer is then decomposed or observed forcing the quantum state into a final and complete solution. Some quick info for those who have no idea what qunatum anything is... an observation is essentially defined as any force that forces a quantum state to be amplified into a definitive state. Quantum entanglement occurs when two paritcles intereact for a short period of time (i.e. two photons crossing) and then go off on their own, they can travel to oppisite sides of the universe and whatever happens to one, instantaneously happens to the other. Literally, no moment of time occurs between the change, its quite amazing. If you polarize one photon, the other will instantly be affected. Also if particles A & B are entangled and C & D are entangled then if B entangles with D then A automatically becomes entangled with C. This allows for some truly amazing things. One final note, although quantum entanglement was first observed with laser light(photons), it has since been reproduced with much larger particles including ruby atoms and even bucky balls (google it if you dont know what one is)
Regards,
Steve

Re:Analogue vs Digital

[jfern]

With n classical bits, they can be of 2^n possible states.
With n quantum qubits, they can be any normalized (overall phase doesn't matter) complex vector in 2^n dimensions.
However, when you measure them, the wave-function will collapse (unless you believe in the many world's multiverse), and you'll get n classical bits.

Classical information is simply a subset of quantum information.

Re:Analogue vs Digital

[natmsincome.com]

Not so much Analogue vs Digital but rather Serial vs Parallel.

In searial you do one instruction per peice of data. In parallel you try EVERY piece of data in one instruction.

Some problems are trivial in serial but hard in a parallel and other problems are trivial in parallel but hard in serial.

Simple Example:
Iterative calculation are great in serial but aren't that good in parallel as you can calcualte the second value till you have the previous value.

The Famous example:
The big thing that quantum computers will do is make parallel problems trvial. The big two being simulations and cryptology. Cryptology is only hard because you have to try so many different combinations. Quantum would allow you to try EVERY combination at a single time. This make encryption almost useless at any key length.

It's also usefull for simulations like ray tracing and vector maths where you have a complex eqation where you just have to run for every possible variable.

So ever is a single iteration takes 1 hour for a quantum computer instead of 100th of a second for normal computers it will change the world. Breaking a key 2048 bit key will take exactly 1 hour instead of million+ years. Rendering a frame will take 1 hour on a single computer instead of 4 hours on 1000+ computers.

That being said it would be useless for Word, Excel or Firefox :-)

Imagine a quantum computer that does 5 Hz out perform a cluster that does 5 TeraHz.

Re:Analogue vs Digital

[Medevo]

Somewhat, but you are a little off.

The best way I have found to think about quantum computations is that digital computers think in 1's and 0's

Quantum computers allow you to ad "decimal places" to this traditional logic (0.1, 0.2, 0.9, 1.0). As you increase the number of quantum bits, instead of just increasing the number of calculations a second you can do (like with our processors today) you are in fact adding new more "decimal places" by simply looking at the qubits in terms of accuracy. Even a simple quantum computer of 30 or 40 qubits could theoretically out power any single processor today depending on the quantum accuracy involved.

Medevo

Re:Analogue vs Digital

[jfern]

Quantum computers aren't quite as powerful as you make them out to be. At the end of your algorithm, you have to perform a measurement, and each qubit when measured only gives you 1 classical bit.

It's been proven that quantum computers are no better than classical computers at sorting (both O(n log n), although they are better at finding something in an unsorted database (Grover's algorithm does O(sqrt(N)), instead of O(N) classically).

No one has proven that quantum computers are faster than classical computers for factoring. We just know of a fast algorithm for a quantum computer and not a classical computer. It's likely that quantum computers are much faster there, though.

Re:Analogue vs Digital

[Medevo]

The limit of computing is, as you say, on the developer's side, no argument here. It its at least partially reasonable that when quantum computers become more available, that ingenious developers will find ways to squeeze out more power.

Moreover, at the end of the day, you still extract bits from qubits. While one day in the distant future we may be able to interact computers entirely in a quantum environment, but it's a long way off.

The real potential in quantum computers is the problems of density, power, and heating, that have plagued development of faster CPU's seem to apply on a lesser scale to quantum circuits (not that they don't have there unique problems). At the same time, quantum computers could/would suffer a lot less problems with bandwidth/time delay (light/QE info transfer).

Traditional MOSFET based transistors, while powerful (look at today's advanced chips) have been around for a while; there is no harm in looking for something new and better.

Even if quantum computers provided a liner growth curve in processing power to qubits, we could expect a greater throughput in it (due to above stated factors).

Medevo

Re:Analogue vs Digital

[spacecowboy420]

OK, maybe I'll sound like a jackass, but I gotta ask anyway. It seems to me that if you can reproduce entangled particles reliably, and you have, lets say two hosts, both with one half of the set of the entangled particles. If you were to manipulate the state of one set, and that immediately affects the state of the entangled partner on the other host, wouldn't that be the effectively TRUE wireless communication. One where the rate of communication is limited only by how fast you could read and process the set of particles that are local? Wouldn't that be as secure as it gets - media to intercept? Sure, there would need to be software to interface with the states based on the input from the hosts - but if you could do this, you could control the mars rover in realtime. Is this where this is headed, or am I confused?

Re:Analogue vs Digital

[Scorillo47]

Note that entanglement is just one approach in building quantum computers, and it is not really the ONLY approach.

Generally, a quantum computer consists in several quantum systems (for example captured particles, etc). The (quantum) state of these systems varies according to a well-known equation, called the Schrodringer equation. This is a very simple equation that describes the evolution of the system (the derivative of the current vector state) in respect to the current current state & time.

The nice thing about quantum computers is that they operate with multiple simultaneous states, therefore achieving some sort of parallelism. Basically a quantum system can be considered to have a superposition of states - it has two states at once if you want. Some of these states might converge to the same state depending on the hamiltonian or on the external interactions.

The hard part is that you never know when such a computer stops its calculation since the transformation state is fully reversible and goes on ad infinitum. If you want simply to test if the computer reached the end of the calculation, you will affect the current state. Anywyay, this challenge plus many others (for example the precision of the measurement, etc) makes quantum computing very challenging.

Still, there is a theoretical possibility that you can get a high degree of parallelism in certain configuration. A classical result from Shor (you can search on Google) shows that one of the classic problems in arithmetic - integer factorization - can be done in a polynomial time on a quantum computer. This simply means that RSA encryption can be potentially broken, irrespective to the length of the key. But we are still safe - so far nobody built a working quantum computer that would carry on simple calculations like factorizing the number 15.

On the other side, entanglement is an interesting quantum fenomenon which works like this:
1) First, you have to have a way to build pairs of entangled particles. There are several ways to do this, for example by having any quantum process that generates a pair of photons.
2) Second, if you modify the vector state of one particle, the vector state of the other one will be equally affected, regardless of the distance between these two particles!

What's interesting is that entanglement guarantees instantaneous quantum state change therefore contradicting somehow the theory of special relativity. This theory says that events cannot be 100% simultaneous if they occur in different points in space - there is a timing separation based on the particular reference chosen. Practically, no standard matter interaction can be faster than the speed of light.

But there is an exception here - "collapsing the vector state". If you measure the state of a particle, its state will collapse along one of the measured dimensions (according to certain probabilities). The corresponding entangled particle will suffer a similar change, so if you measure now the state of the this second particle you will see that its vector state has already changed - and you can even perform a partial correlation between the results of the two measurements.

In conclusion, enanglement guarantees instantaneous "interaction" regardless of the distance between these paired particles (this is why Einstein called it "spooky action at a distance" - because technically it is propagated with infinite speed). Anyway, it has be proven a while back that this does NOT contradict the special theory of relativity since this is not a standard matter interaction, like gravity, etc.

Going back to computers, entanglement is an interesting approach which might enable new algorithms or new ways to build such computers. But keep in mind that we are in the stone age of quantum computing right now...

Re:Analogue vs Digital

[cicadia]

Well, you're not a jackass, but it is a bit more complicated than that. Unfortunately, there doesn't seem to be any way to actually transmit information instantaneously with entangled particles. It's true that two entangled particles will undergo the same transitions at the same time, but since you can't predict in advance or control what transition will occur, it doesn't help you send any information to a person looking at the particle at the other end.

You're right, though, that it's about as secure a communication channel as you can get. It's actually the basis for quantum cryptography -- two people share a set of entangled photons, and they can guarantee that the measurements they make on them will be identical, giving them a shared secret key that no one can intercept. They still have to communicate over regular channels to actually send any real information, though.

Re:Analogue vs Digital

[little_prince]

I don't understand rather can't (no background on quantum physics) - how can *same thing* happen *instanteously* to two entangled-in-past particles at opposite sides of the universe. Something happened to one, this information has to transfer in some way to other, even if it happens at the speed of millions times speed of light (is is possible that anything travels faster than light does??) it can't be instantaneous! Looking at the amazing possibillities of trying out many possible solutions at once with quantum physics, I guess it will find good usage with genetic algorithms.

Re:Analogue vs Digital

[dave1791]

A slightly off topic anecdote; back when I was in grad school, one of the professors in my department jumped from stat mech to qc. I clearly remember his first talk when he started getting into qc. He said "Ooooo, this is bullshit"!.

Then when he discovered that he could score a bazillion dollars in grant money, he said "Ooooo, I think there is something to this"!.

Re:Analogue vs Digital

[aka-ed]

Think of twins separated at birth, both with a love for brussel sprouts. Nothing travels between the two. The particles commune more than communicate.

Re:Analogue vs Digital

[aka-ed]

Are you saying that you think QM is BS?

If not, are you certain it was grant money and not closer examination of the premises that caused the prof's conversion?

Re:Analogue vs Digital

[pikkumyy]

So, if I'd have two donuts that have their atoms entangeled, and I'd eat one, would it increase my bodyweight twice as much, since the other donut would have gotten eaten by me instantly also?

If not, and these two share the same state, if I would eat one and after swallowing all the fat would be vaporized somehow from the un-swallowed one, would that allow me to eat as much as I want?

Regards,
Homer

Re:Analogue vs Digital

[Jeffv323]

So far, I haven't seen this explained... What if you had two entangled particles, one on say, the Mars Rover and the other back at NASA. Why isn't it possible, to set up an instant line of serial based communication using a system of Changed or Not Changed. Changed being a '1' and !Changed being a '0' You sync the clocks on the rover and back at NASA, and just manipulate the particles at 9600bps!
I'm going to attempt to answer my own question here and guess that the reason this form of communication is not possible, is because as soon as the particle's state is read, the state changes?

Re:Analogue vs Digital

[jfern]

If you have an entangled EPR pair, measuring one collapses the other into the same state. You can share random data, not useful for transmitting information.

The quantum teleportation technique relies on you sending classical information that doesn't break the speed of light limit.

Re:Analogue vs Digital

[Anonymous Coward]

Sice you can't predict if it collapses to 0 or 1 you get random information.

Re:Analogue vs Digital

[dave1791]

I am not saying that I think qc is BS. Not at all; in fact, when theorists gave (not at uni anymore) talks on the subject, I rarely missed them.

As a former experimentalist, I realize that qc is very hard to DO. I am not close enough to the field to say whether is "fundamentally not practical" hard to do, or just "takes a lot of hard work" hard to do. It is still worth researching in any case.

I am cynical enough about academic research and the way that researchers follow the grant money to be unsure about this particular researcher's motives. It may be that he decided that qc was exiting enough to do on its own. I saw a guy stick to his work even though he did not get any grants for many years because he was deeply interested. I was rather pleased to hear recently that he got a couple of nice grants and has a couple of RAs now. I saw a guy move to biophysics (another fashionable field) because there were problems that intrigued him.

I have also seen researchers whore for grants in a big way. Academia is about ego. Publish or perish! Without grant money, it is difficult for an experimentalist to do anything worthwhile. It is not so bad for theorists, but grant money still pays for graduate students (RAs that are on the project full time as opposed to TAs that also have teaching duties) and postdocs. Money simply makes it easier (in terms of manpower and equipment) to do the kinds of things that get you published. The number of publications, and even more so how often you are referenced determines you stature in academia. An unpublished professor is a nobody out in the wilderness. Science has its fads, just like the worlds of business, music and fashion. These fads tend to manifest themselves in the form of where the grant money is.

Re:Analogue vs Digital

[Hieronymus Howard]

This simply means that RSA encryption can be potentially broken, irrespective to the length of the key. But we are still safe - so far nobody built a working quantum computer that would carry on simple calculations like factorizing the number 15.

How do you know this for certain? If the NSA's scientists have cracked this you can be damn sure that they're not going to tell anyone about it.

HH
--

Re:Analogue vs Digital

[WoodenRobot]

Check out this on theEPR paradox.

Re:Analogue vs Digital

[Anonymous Coward]

It is important to note that although observing one entangled particle can effect another some distance away simultaneously, there is no way use this quirk to _transmit information_ simultaneously.

It's not like you could entangle some particles, travel to Alpha Centuari and then observe them in some sequence to "send a message" back to earth. Yes the ones on earth would be affected instantly, but an observer on earth would not be able to infer any meaning out of it or know that they had been observed.

Re:Analogue vs Digital

[wass]

Wow, 2 quantum computation articles on /. within two days.

I mentioned this yesterday as well, but for an idea of what qubits are you can take a look at my currently unfinished Java Quantum Computation applet. As of now one can only do single-qubit operations, but eventually I hope to have a demo of quantum teleportation (teleportation of a single qubit, or spinor, that is).

This applet will give you an idea of what qubits are. Essentially they're a 'spinor' which in quantum-mechanical terms is a 2-element discrete wavefunction. In lay terms, this just means a set of two complex numbers (properly normalized). They are also displayed in a more visible representation, called the 'Bloch Sphere'.

This applet will let you take any input qubit, and operate on it with 6 different single-qubit quantum gates, and see the resulting qubit.

Look at the two qubits represented on the Bloch sphere. The yellow vector represents the qubits. The red dot indicates a classical 'zero' and the blue dot indicates classical 'one'. In classical computing any bit can only point exactly to the red or blue dots. In quantum computation a qubit can point anywhere on that sphere.

[For the mathematically curious, a qubit is 2 complex numbers, which would be 4 independent parameters. However, the sum of the modulus squared of each complex number must be unity, so that constraint leaves only 3 free parameters. Secondly, the entire qubit can be multiplied by any arbitrary phase constant (e^i*gamma) which changes the spinor but not its relative values. Hence, there are only two parameters for each qubit that really matter, so it can be expressed in 2D, mapped nicely to the sphere.]

In classical computing there are only 2 single-bit gates - Not and Buffer (actually, I never formally studied computer science, so someone please correct me if this isn't true). 'not' flips the bit, 'buffer' keeps the bit unchanged. In quantum computing there are infinitely many single-bit gates, some of the common ones are demonstrated in the applet. Basically, these gates can control how relatively 'one' or 'zero' the bit is by the superposition, as well as change the relative phase.

Anyway, I should be adding in two-qubit operations soon (like the infamous controlled-not) and hopefully get to something worthwhile.

So this applet isn't very useful for actual simulation of quantum computation yet, but it will you give an idea of what qubits are and how they can be represented.

Re:Analogue vs Digital

[Scorillo47]

Correct - there is no way to transmit pure information through photon entanglement for example. But it is possible to use this technique to verify some information transmitted in conjunction with a separate (classic) channel.

This has two consequences:
1) First, it is practically possible to use entanglement to build networks that are 100% guranteed to transmit either correct information or error.
2) Second, since measuring any particle will necessarily change it state gives an interesting conclusion: it is impossible to tamper the communication channel that transmits entangled photons. As soon as you attempted to measure what's on the channel, the verification mentioned above (i.e. the correlation between the final measurement of the two entangled particles at the two ends) will fail!

Therefore you have a bullet proof method that will prevent active/passive attacks on the entangled channel. The technique was actually employed in practice - see this link for example.

NB - this technique still doesn't prevent attacks that fully substitute one of the ends with a completely identical device so the other end still thinks it is talking to the right person. But in combination with standard cryptography techniques for the insecure channel, this techniue is almost impossible to break. A nice overview is presented here

Re:Analogue vs Digital

[Anonymous Coward]

Hey, we can't entangle donuts yet, just photons and ions.

(Well, maybe atoms, but not very complex particles like donuts and teapots.)

So, if you eat a donut full of entangled atoms, nothing happens to the atoms nor to their pairs. It doesn't even taste funnier.

Still tastes very good, though! (I did notice the signature...)

Re:Analogue vs Digital

[essreenim]

If you have an entangled EPR pair, measuring one collapses the other into the same state. You can share random data, not useful for transmitting information.

It actually has more potential than this. It is not random, if 'measured' properly. This is the whole philosophy of Quantum communication, which in my opinion is actally the most interesting theoretical aplication of Entanglement.

Whats preventing development is the ability to reliably and measure and remeasurean entangled pair without affecting certain properties of it s twin. Hence the whole paradox of changing the nature of a photon by measuring some of that photon -hence removing any value from the measurement in the first place. But it is possible to measure a photon without altering it. You may remember experiments in Paris using iridium to actually measure the change in phase of the iridium that is fired into the photon, not measuring the photon itself, but rather a relatively acceptable phase change in the iridium. Now as I understand it, the main problems are that scientists can slow down and even completely freeze a photon of light, as demonstrated by a Dutch scientist. Then the technology is there to measure this 'frozen' photon repeatedly. As far as I know, its just not reliable enough yet...

As for Quantum teleportation (which really is more quantum replication than teleportation) many many years await before it can be applied usefully on a large scale. Same almost for Quantum computers - though they may arrive sooner than we think)

Re:Analogue vs Digital

[Kallahan]

Probably redundent, but there are no such things as ruby atoms, only ruby molecules.

Re:Analogue vs Digital

[plaa]

Even if quantum computers provided a liner growth curve in processing power to qubits, we could expect a greater throughput in it (due to above stated factors).

See my post a little below. Quantum computers can make some problems blazingly fast to solve, while not giving any advantage to others. Considering that classical computers have been developing for some 30 years, it'll be a very long time before quantum computers can come even close to matching classical ones for problems not specifically suited for quantum computing.

My guess is that when quantum processors become commercial, they will for a long time be number-crunchers controlled by normal computers, and later (when/if they become mainstream) as an add-on to normal computers, just like the FPU's were in the 80's and 90's. I really don't expect to see a quantum-computer driven desktop in my lifetime.

Re:Analogue vs Digital

[maxwell demon]

Whats preventing development is the ability to reliably and measure and remeasurean entangled pair without affecting certain properties of it s twin.

You cannot measure anything without affecting it. That's one of the basic properties of quantum mechanics. Especially, if you have an entangled pair, and measure one parner, then you destroy the entanglement. Always, and inevitable.

Even if you try to circumvent it by first having it interacting with something else and then measuring that other thing: If by measuring that other thing, you get information about the partner (more exactly, about the value of one observable of that partner), then it means the "circumvention system" was included into the entanglement, and your entanglement will be gone as soon as you measure that.

Worse, measuring the original entangled pair without the "circumvention system" will have them behave as if they already had been measured, that is, you cannot make use of that entanglement without having access to all systems which take part in it, which now includes the "circumvention system". Actually, that's how decoherence works: The interaction with the environment causes the environment carrying information about the system ("measuring" the system), and therefore destroying coherence since you cannot completely know/control that environment.

Re:Analogue vs Digital

[shambalagoon]

How can two photons clear across the universe communicate instantaneously?

One idea I've heard is that they're actually just ONE photon, showing its face in two different points in spacetime simultaneously.

And regarding the challenge of getting information out of quantum-entangled particles, if we could get the Dutch freezing process down, we could: alter-freeze-read-alter-freeze-read

Re:Analogue vs Digital

[dazilla]

I still fail to see how you cannot "transmit" the information at greater than the speed of light. Of course, I know that due to special relativity, this is impossible. But, if you specify a certain "state code" before one entangled atom is taken to Alpha Centauri, and then use the "state code" to affect the state of its entagled atom on Earth, why is this not transmitting information? I mean shouldn't you be able to say: ok, this state means this, another state means that, etc etc. (and I realize the message would be destroyed the instant it's read), and then change the state of the distant atom into the appropriate states to transmit a message?

Re:Analogue vs Digital

[doug363]

If you want to be pedantic, there are four different classical one-bit input and output gates (because each of the two possible inputs has two different output possibilities, and 2^2=4). They are the Not gate, the Buffer gate, a gate that always outputs one regardless of its input, and a gate that always outputs zero. The latter two aren't terribly useful as gates -- you don't need the input at all. So you're pretty much right: there are only two useful classical single-bit input and output gates.

Re:Analogue vs Digital

[aka-ed]

Thanks for the clarification.

I share your cynical view wrt academia and $, but individual researchers don't have the means to change the influence of market forces on the field as a whole; it's hard to be sure when anyone is "ho'ing."

One could argue that, when market forces draw researchers to a field of such potential, such forces are working the way they should.

Re:Analogue vs Digital

[CodeMonkey4Hire]

What's interesting is that entanglement guarantees instantaneous quantum state change therefore contradicting somehow the theory of special relativity. This theory says that events cannot be 100% simultaneous if they occur in different points in space - there is a timing separation based on the particular reference chosen. Practically, no standard matter interaction can be faster than the speed of light.

I don't see how this is 100% simultaneous. Let's say one pair breaks down. We call that event A in the observer X's IRF. Then another pair breaks down - event B. Let's use A as our reference point. An observer Y in a different IRF will say that event B did not happen at the same time oberver X said it did. There will be a difference in the time elapsed.

Am I looking at this wrong? I can picture a different way of looking at it, maybe you can give me the answer:
Particle A and B are entangled. Let them be 1 lightyear apart. When the state changes, observers of each particle send a signal to each other. The observer at A gets the signal about B one year later. The observer at B gets the signal about A one year later. I don't see how anything really changes by adding in a bunch of IRFs.

Please elaborate. Wikipedia is interesting, but doesn't go into detail about simultaneity.

Re:Analogue vs Digital

[ganhawk]

Let me try to explain quantum teleportation whith what I know of it.

There is no equvvalent macro phnenomenon for quantum teleportation. But let me try this example.
Quantum teleportation is something like this..

If you have a metal box that can be broken into two metal boxes. Initially there are two colored balls in the metal box. You cannot see the balls. When you break the box into two, each ball stays in one box. You can now seperate the box by a large distance. This pair of boxes is similar to entangled pair. By obeserving the first box, you can determine the color of ball in the second box.

At the quantum level, without knowing the color of the ball, it is assumed to be in a state of superposition. so Observing the first photon forces the state on the second photon.

Re:Analogue vs Digital

[pboulang]

If you take into account the fact that scientists require a minimum of something like 10 dimensions to make the equations work, and then extrapolate the 2D->3D folded paper concept (points far away on the paper can be made close by utilizing the "extra" dimension) into 3D->4D, it can be seen that possibly points that seems very remote can be very close indeed.

Re:Analogue vs Digital

[GuyWithLag]

No, because you cannot force the outcome of the correlation, which is always random. However, it will be the same random stream for both the local and the remote instance. You can then transmit the information XOR'ed with the random signal over classical, slower-than-light methods. The recipient goes on to decode the signal using his own random stream. If the resulting signal is random noise, the information has been tampered with.

Re:Analogue vs Digital

[kerrbear]

they can travel to oppisite sides of the universe and whatever happens to one, instantaneously happens to the other. Literally, no moment of time occurs between the change

I ask, could it be possible that this could be used as some kind of communication system across space. If some alien race were to affect particles in their space, then previously entangled particles corresponding to them (like from soon after the big bang) would be affected in other parts of the universe. If we could detect and decode those particles we could pick up messages.

Is this just crazy thinking or might there be some vast network out there waiting to be found?

Re:Analogue vs Digital

[drgonzo59]

By "instantaneously" it is meant really instantaneously, not just speed of light fast. A bad example might be if someone puts two colored tokens, a white and a black one, in a bucket and shufles them, then you and your friend both take one without knowing which color you took. Then you fly to Chile, while you friend stays in Kathmandu. When you arrive, you look at your token, if it is white, you instantly know your friend has a black one. EXCEPT that in the quantum world if you happened to find you carry a white one , your friend's token, wherever he is, will actually CHANGE at that instance when you looked at yours. That is why the example is not perfect, just give you some idea.
And the most importantly, the color of your particular token was not determined when you took it from the bucket but when you looked at it. Now to translate to the physics terminology:
tokens = particles
white/black = bit values (1 or 0)
shuffling = entanglement (through some interaction for example)
looking at the token = measurement
Chile = Chile
Kathmandu = Kathmandu

Re:Analogue vs Digital

[jekewa]

So then I can open my quantum word processor, hit a key, and every letter I meant to type would be there in the right order? Man, that's cool!

Re:Analogue vs Digital

[exp(pi*sqrt(163))]

This isn't completely correct. If you naively look at what happens in a quantum computer it's easy to think that you're running things in parallel - but in the most obvious sense you're not. In fact Deutsch's original paper shows how this naive interpretation of quantum computers doesn't really get you anything. Shor's factorng algorithm doesn't work because it tries every factor simultaneosuly - it works because it uses a cunning variation of the discrete fourier transform to tangle up different potential factors in such a way that non-factors cancel each other out and factors interfere constructively. It's a very special algorithm tailored for a particular problem, not a direct implementation of massive parallelism.

This isn't to say that what you argue is completely incorrect either. For example, if you want to search a database with N entries for one matching a given specification, then on a classical serial machine it might take time O(N), and on a large parallel machine it might take time O(1). On a quantum computer you can use Grover's algorithm and find it in time O(sqrt(N)) (and this is known to be optimal in some sense). So quantum computers are a bit like the geometric mean of serial and massively parallel machines.

Re:Analogue vs Digital

[kmac06]

The (quantum) state of these systems varies according to a well-known equation, called the Schrodringer equation. This is a very simple equation that describes the evolution of the system (the derivative of the current vector state) in respect to the current current state & time.

What Schrodinger equation are you looking at? The one I'm looking at is definitely NOT simple, and even less so to actually solve the equation.

Re:Analogue vs Digital

[hesiod]

> One idea I've heard is that they're actually just ONE photon, showing its face in two different points in spacetime simultaneously.

That's an interesting theory. So if all of the particles that make up my body have an entangled mate (I'm sure it isn't the case, but...), then there would essentially be another me (or at least another image of me at another place -- I would technically be both places) floating in space somewhere mimicing everything I do? Man, some pervert (or his 2nd image) could be out there somewhere watching me sleep. Creepy...

Can you tell I never took quantum mechanics?

Re:Analogue vs Digital

[hesiod]

> if we could get the Dutch freezing process down, we could: alter-freeze-read-alter-freeze-read

Doh, should have comprehended the whole thing before posting a joke -- now I have a serious question. Wouldn't "freezing" or unfreezing the particle change it & therefore its entangled mate rendering it unreadable?

Re:Analogue vs Digital

[hesiod]

> if I would eat one and after swallowing all the fat would be vaporized somehow from the un-swallowed one,

No, the entangled particles would just disperse in a similar way as they do in your stomach. Unless you looked at the donut prior to eating it -- you didn't, did you? Otherwise, it may disappear suddenly, or at least change into a croissant.

Re:Analogue vs Digital

[Scorillo47]

There are several versions of the Schrodinger equation. For example the time dependent one looks like this:

H * v(t) = i * h * v'(t)

where
H = the hamiltonian of the system (if you want, this represents the "hardware")
i = the unit imaginary number
h = the Planck constant divided by 2 * pi
v(t) = the state vector

So basically, the product between the hamiltonian and the state vector is the variation of the state vector in time, multiplied by the constant (i * h)

For more details see this link.

Re:Analogue vs Digital

[Scorillo47]

>>> I don't see how this is 100% simultaneous. Let's say one pair breaks down.

It is simultaneous simply because as long as you don't perturb it, a pair of entangled particles constitute a single quantum system, a single "particle" if you want. As soon as you touch one of them, the pair is broken and now suddenly you can imagine having two separate particles popping up in space at certain distance between them.

>>> We call that event A in the observer X's IRF. Then another pair breaks down - event B. Let's use A as our reference point. An observer Y in a different IRF will say that event B did not happen at the same time oberver X said it did. There will be a difference in the time elapsed.

No. The state vector collapse is not an observable event in itself. Only the measurement is an observable event. All you can do (as observer X) is to measure both particles and hope/presume that the collapse already hapened - but you have no 100% guarantee that of course, unless you setup the experiment in certain ways.

>>> Particle A and B are entangled. Let them be 1 lightyear apart. When the state changes, observers of each particle send a signal to each other. The observer at A gets the signal about B one year later. The observer at B gets the signal about A one year later. I don't see how anything really changes by adding in a bunch of IRFs.

Of course, the outcome of the measurement depends on the state of the entangled pair and the type of the measurement. But there will be always a certain non-linear correlation between the two measurements done by observers at A and B. This means that the measurements were already correlated before the observers could possibly communicate. How would you explain this correlation? The actual measurement happened one year in each IRF before getting the data from the other observer.

Here is a more detalied explanation.

Re:Analogue vs Digital

[shaitand]

So why can't you simply use the frequency of collapse (which you can control) rather than the collapsed state itself as "the data"? Poll in fixed intervals.

Or another way (just based on what I've read in this thread thus far) would be the number of particles which have collapsed composing the value.

With either method it doesn't matter what the actual state of the particle is, so long as it's different from what it was before right? As for the fluke possibility of it actually being what it was before... well standard error correction algorithms and protocols should pretty much resolve that.

I'm sure there is some reason neither way would work that I'm ignorant of. But from anything I've read here or elsewhere I can't imagine what. After all, it wouldn't be instant per say and there would be extra overhead this way but, the polling frequency should be settable to whatever we want, and we'd be able to receive data much faster than we can process and interpret it.

Re:Analogue vs Digital

[king-manic]

Like the communicaiton devices in Enders game. Ansible. This could make space flight more reasonable. Instant communicatiosn back with home base. and robotics too. No lag or latency between communications.

Prime Intellect?

[Anonymous Coward]

Isn't this the correlation effect mentioned in the prime intellect story?

In the PI universe, a Beowulf cluster of these imagines YOU!

Re:Prime Intellect?

[Azrael Newtype]

Wow, combined the obligitory Beowulf cluster joke with the obligitory Family Guy reference. Good job.

Re:Prime Intellect?

[Anonymous Coward]

No, idiot, a reference to localroger and Kuro5hin!

can someone qualified answer this question

[Anonymous Coward]

Just say 20 years from now I am on my quantum fandangle computer that does sub-atomic calculations, what happens when background radiation hits the processor and flips a few 1s and 0s?

i.e. will my computer crash when there is a solar flare?
will the new "heatsinks" be lead shields?
will we need to rotate the shield harmonics? (j/k)

please... inquiring minds want to know.

Re:can someone qualified answer this question

[phoenix.bam!]

I'd have to say (not that I actually know) that there would be equal danger now from a solar flare crashing your computer as there will be on a quantum computer. But what the hell do I know? You should go ask Scotty.

Re:can someone qualified answer this question

[Anonymous Coward]

Scotty's busy trying to talk to the mouse.

"HELLO COMPUTER"

Re:can someone qualified answer this question

[jfern]

The problem with quantum information is that you can't clone (copy) an arbitrary quantum state, and you can't measure an arbitrary state without destroying the quantum information.

However, there still exist quantum error correcting codes that can correct an arbitrary error. Classically, one only gets bit flip errors. In quantum computation, you have to worry about phase flip errors, for instance instead of a|0>+b|1> you have a|0>-b|1>.

The smallest quantum code that can correct an arbitrary non located (located errors are easier) error on 1 qubit requires 5 qubits. There's a 7 qubit "CSS" code that is important for fault tolerance.

For fault tolerance, you concatenate a code with itself many times, and if your errors are independent of each other, then by doing all sorts of complicated fault tolerant techniques, you can get fault tolerance. What happens is you get a fault tolerance threshold. If your rate of errors are less than that, you can do arbitrary quantum computation with O(M) qubits in O(N polylog N) time, where O(M) is the qubits required on an error free quantum computer, and O(N) is the time required on an error free quantum computer.

Re:can someone qualified answer this question

[Muqtada al-Sadr]

Allah is the answer!

Re:can someone qualified answer this question

[nihilogos]

Just say 20 years from now I am on my quantum fandangle computer that does sub-atomic calculations, what happens when background radiation hits the processor and flips a few 1s and 0s?

Quantum error correction. is a sub-field of quantum computing concerned with just that, how to effectively perform a quantum computation in the presence of background radiation and other stuff which sub-atomic thingies tend to be quite sensitive to.

The likelyhood of flipping a few zeros and ones ( and other errors which can afflict quantum bits) is very high, and in reality is more a continuously decay than an instant flip.

It has been shown, however, that this continuous decay is equivalent to flip errors and phase errors (the other sort of quantum error) occuring with some probability. That probability is 1 in 10 for most of the current experiments, compared to your box in front of you which is more like 1 in 10 billion.

Fault-tolerant quantum computing is a theory field of research concerned with how good quantum computers have to be before quantum error correction can work. The best results at the moment suggest a probability of error of 1 in 1000 is good enough. The experimenters have a fair ways to go yet.

Re:can someone qualified answer this question

[jfern]

Some of us are working on getting a better result than 1 in 1000. ;) Actually, the important thing is, it depends on what sort of noise you get from your gates.

Re:can someone qualified answer this question

[Kiyooka]

Even if that happens, you'll get used to it and just reboot again. If there's one thing that'll never change, it's the complexity's and problems that new technologies bring with them.

Re:can someone qualified answer this question

[mcrbids]

That probability is 1 in 10 for most of the current experiments, compared to your box in front of you which is more like 1 in 10 billion.

Would you really think even a e-machine is that error prone?

Think about it...

2.5 Ghz * 32 bits/cycle = 80,000,000,000 - that's 80 BILLION bits per second...

Of course, that's theoretical, there's buffering delays, cache, noops, etc. But, given the theory, there'd be 8 random errors every single second.

Something doesn't sound quite right, here, especially when you figure the vast majority of computer are sold with no error correction at all on the system memory ?

I think that 1 in 10 billion is probably quite a few orders of magnitude off....

Re:can someone qualified answer this question

[Myolp]

My guess is that there will be something similar to SCSI LVD. Since the decay of two nearby particles should be roughly the same, the real value could be decided from the differential value of two particles.

But what do I know? I'm just a bum with a masters who spends his working hours on /.

Re:can someone qualified answer this question

[jrockway]

More like "Psssssst. Hey you. Yeah you. Who do you think I'm talking to... the mouse!?".

What might this be a reference to? :)

Re:can someone qualified answer this question

[Epistax]

Just say 20 years from now I am on my quantum fandangle computer that does sub-atomic calculations, what happens when background radiation hits the processor and flips a few 1s and 0s?

This happens now, actually. We can't stop it entirely, but we can lower the chance that it happens in our modern chips. The funny thing about this problem is that it's usually not a problem. Take a Pentium 4 and flip some bit somewhere in it. Worst case is it'll cause the system to halt (parity checks prevent most bad data from leaving the chip). However just as easily it may take literally years of running the chip without reset for you to ever see the error that was caused, or never. I don't know about you but I don't particularly care if my 286 compatibility goes awry. Even under a fully utilized chip (performing common instructions non-stop) the majority of the chip is usually not be being used. Basically not only does a bit have to be hit, it has to flip. It also has to be at the correct part of the clock cycle such that its value will be read and make it to the next flop. That area of the chip must also be being used. Internal protocols used may even be prepared for mismatches such as this, causing things just to be redone.

Intel and another corporation (Motorola?) recently announced a cutback in lead in their designs so I don't know if they'll put a big chunk of it on for quantum computers. Perhaps they won't have a choice.

Re:can someone qualified answer this question

[Kallahan]

He was choosing an arbitrarly large number, but that was pretty nteresting any way.

Re:can someone qualified answer this question

[Anonymous Coward]

Error correction is already completely necessary to get good results in a quantum computing system. The "fidelity" that is specified is essentially how error free the experiment is-- You'd like to see a fidelity of 100%, but present experiments are nowhere near that.

For trapped ions, the dominant causes of poor fidelity are heating of the ions in the trap by surface potentials and spontaneous emission induced by the laser beams used to produce the Raman transitions between different internal states.

There's a long way to go to 100% fidelity!

Re:can someone qualified answer this question

[ithicine]

That probability is 1 in 10 for most of the current experiments, compared to your box in front of you which is more like 1 in 10 billion.

The future of debugging: "Try it now! No? Okay... try it now! No? ..."

In other news, mass numbers of quantum computer programmers suddenly develop gambling problems....

Re:can someone qualified answer this question

[Klebz]

"Beam me up Scotty" "Damn it Jim, im giving er all shes got"

Re:can someone qualified answer this question

[nihilogos]

Yep, it probably is quite a few orders of magnitude off.

I definately hope that my hard drive controller has some error correction built into it though :P

Re:can someone qualified answer this question

[Anonymous Coward]

Actually, (I believe I read about this in one of Feynman's lectures on computing), the probability of errors in classical computers is related to the voltage moving the transistors and the distance the transitors travel. Based on these factors, a computer should not experience this type of error in your lifetime, and definitely not in the lifetime of the computer.

Re:can someone qualified answer this question

[cazzazullu]

auw, now I have a headache. Shouldn't have read your post :S

Re:can someone qualified answer this question

[nihilogos]

"Some of us" meaning yourself, Ben, and Umesh I am guessing ;)

Teleportation

[Naffer]

So we've got the one atom thing down now. The trick is getting a whole lot of atoms to do it at the same time. If we can convince the porn industry that it would be beneficial to them, We'll be teleporting around the world in less then 5 years. Maybe I should patent teleporting prostitutes.

Re:Teleportation

[DigiShaman]

Offtopic...yes. But I find this to be insitefull. When all else fails to fund a project, love to the desires of human nature and those with capitol to spend. Seriously, if a "holodeck" were to ever be built...look to the porn industry to lead the way. Then, the technology will find it's way in other niches.

I'm not sure if this is sad, but it's reality of human nature that connot be overlooked as a method for expanding scientific knowledge.

Re:Teleportation

[DigiShaman]

Umm, how about paying for INTERNET BANDWIDTH. Do you even KNOW how much the porn industry pays for bandwidth. Basically, unmessurable amount the way I see it. So the more they pay for the infrastructure, the cheaper it will be for all of us geeks in the long run. I hate to break it to you my friend, but sex and the prospect there-of is the primary foundation for our society. It's basic evolutionary psychology.

Re:Teleportation

[Kiryat Malachi]

Let's see...

I see you, and raise you the videocassette, the home video camera, the DVD, e-commerce, and online payment systems.

The videocassette and DVD? Both were driven by porn (VCR more than DVD, as DVD was more an evolution - but porn is one of the few users of "multiple angles"). Seriously, look at the history. Home video cameras? Amateur porn!

E-commerce was basically invented by porn. Online payment systems, the same.

Like it or not, porn does tend to drive some technology's adoption into the mainstream.

Re:Teleportation

[king-manic]

Since it's imprinintg properties it's more like duplicating. Imagine duplicating the celebrity of yoru choice to spend the night with. Knowing Quntum mechanics, You pick randomly a box of names and you won't know who it is until you wake up the next morning and when you find out they disappear is a flash of neutrinos.

Re:Teleportation

[king-manic]

Video streaming. Pushed the comsumption of bandwidth up and thus the per capita price of bandwidth down. Principal economic force behind the expansion of the internet. at least for brining more web hosts into exsistence. Lead the charge in e-commerce. Security and fuctionality was pushed by the industry. They don't specifically create technologies. Only provide a huge market place for them and thus incentive to create such technologies. companies like IVista appear to specialize in Tele-Confrencing but actually make most fo their money supplying software to cam girl sites.

One of the few companies that actually does it's own coding for applicatiosn is IFriends. They write their own video chat streaming programs and servers. And credit companies on the net Generally made their money through Porn site.s CCbill. MyPaysystems. And hundreds of others.

Yes, fast

[Milo of Kroton]

But what cost? Only government would want new technology this fast, maybe your NSA, that around codebreaking.

Re:Yes, fast

[tachyonmkg]

Only the five richest kings of Europe will be able to afford them.

Re:Yes, fast

[Anonymous Coward]

Well the NSA are centainly funding QC programs.

Also scientists will want QC's to do complex simulations

Re:Yes, fast

[jfern]

"We see a worldwide demand for maybe a couple of computers" - IBM
"640k of memory is enough for anyone" - Gates

Re:Yes, fast

[Bl33d4merican]

Only government would want new technology this fast, maybe your NSA, that around codebreaking.

Only the government would want it? Hell, I'd want it! Who wouldn't?

Re:Yes, fast

[techno-vampire]

Yeah, right. We'll only need a few quantum computers just like we only need a few computers. Thank you Mr. Watson of IBM.

Re:Yes, fast

[Anonymous Coward]

someone help us understand this one. some illuminati joke?

Re:Yes, fast

[aka-ed]

"Uh, Sure, the Frinkiac 7 looks impressive. But I predict within that one hundred years computers will be twice as powerful, ten thousand times larger, and so expensive that only the five richest kings of Europe will own them." -- Prof. Frink, The Simpsons

Perhaps the only way I can make a positive contribution to a discussion of QM.

Re:Yes, fast

[Anonymous Coward]

Thanks!

Re:Yes, fast

[plaa]

Comparing the speed of a quantum computer and classical computer is comparing apples and oranges. Quantum computers work with a totally new set of rules, which allows some applications to make use of quantum properties.

The main property that classical computers lack is that of superposition of states. One can understand this as calculating some result starting with all possible numbers at once, instead of testing each starting value as its own. (In reality it's more complicated than this, of course.)

Some applications, eg. codebreaking, number crunching and database applications could get a vast boost out of quantum computing. Other applications may not. The most probable places for quantum computers (at first) will probably be number crunching, networking applications (quantum cryptography etc) and database applications.

For a comparison, searching an unsorted database is classically an O(N) operation, but a quantum computer can do this in time O(sqrt(N)). The best known classical algorithm for factoring a number is exponential, while Shor's algorithm does it in time O((log N)^3) (allowing polynomial-time breaking of RSA).

Re:Yes, fast

[king-manic]

But what cost? Only government would want new technology this fast, maybe your NSA, that around codebreaking.


And nobody will require more then 640k. And the world will need only 10 computers.

Hard to predict what off-beat academic research (lasers) will turn into useful consumer products (cd-players).

Re:Umm...this is old news.

[ikewillis]

Are you sure that wasn't performed with photons? I'm fairly certain this is the first time the characteristics of atoms have been transferred...

Re:Umm...this is old news.

[beeplet]

This is the first time anyone has been able to use atoms (as opposed to photons) in quantum teleportation.

Right on

[Elpacoloco]

I have a very bad conception of quantum computing as it is, I've somehow confused it with the idea of getting computing power out of the atoms themselves. (which is probably as related to actual quantum computing as star trek is to physics.)

Still, this is good. A few more angstroms out of electronics means a few more decades of potential improvement.

Re:Right on

[jfern]

The advantage of a quantum computer, is that we know how to run certain algorithms with a better big-O running time than on any classical computer. It doesn't matter if a quantum computer gets fewer operations per seconds than a classical computer, it'll still win for factoring large numbers.

Now, there's a different field of study called "Rapid Single Flux", where one tries to built very small classical computing devices that take advantage of quantum mechanics, but don't have the big-O advantages of quantum computing.

Here's a link.

Re:Right on

[ithicine]

I've somehow confused it with the idea of getting computing power out of the atoms themselves

We already do this. They're called Computrons

Almost...

[ShatteredX]

...but not quite teleportation (at least as most people understand it).

Re:Umm...this is old news.

[ioslipstream]

Maybe not so old...

http://www.guardian.co.uk/uk_news/story/0,3604,1 24 0489,00.html

How to choose?

[Shambhu]

This wiki looks good, and if it isn't too technical, maybe I can find the answer. However, every other article, paper, or discussion that I have seen skips this one question of mine: How is the choice made between all the superimpositions to select ther 'right' answer? Everyone goes to great lengths to explain the superimposition part and its implications for massively parallel computation, but no one ever says how you choose the result! Does anyone have a clue about this?

Re:How to choose?

[ajayg]

Good question. In fact, this is one of the trickier problems to solve when coming up with a QC algorithm. The trick is, to use the phenomenon of coherent interference to yield the result that you are looking for. Interference here is basically the same as wave interference. So, after our QC executes an algorithm and finds the solution to a problem for all N inputs simultaneously, we then have to interfere our output result state (which now exists as a coherent superposition of N different outcomes) in such a way as to obtain the result we are looking for. A good example you might want to look up is the Deustch-Josza algorthm, which though useless for most practical purposes (in my opinion :-)), shows how we can use intereference in a smart way to obtain the desired result.

Re:How to choose?

[skifreak87]

It's my understanding that this is the hardest part of quantum algorithms. It's quite straightforward to just pick one answer and so with fixed probability (based on size of system) answer is right, otherwise it's wrong. IIRC, the beauty of shor's algorithm (factoring in polynomial - linear i think - time on a quantum computer) is that it always returns the correct answer. Unfortunately I don't know how it works so I can't answer that part. i hope someone else can explain that.

Re:How to choose?

[jfern]

A typical quantum algorithm puts most of the wavefunction into the state(s) that you want. By applying various quantum unitary gates repeatedly one can do this. It's kind of hard to explain exactly "why". One then measures the state, and with with probability p gets a correct answer. If p> 50%, one can repeat the algorithm a bunch of times to make sure one has the right answer.

Re:How to choose?

[skifreak87]

Sorry to reply again but from wikipedia
Like all quantum computer algorithms, Shor's algorithm is probabilistic: it gives the correct answer with high probability, and the probability of failure can be decreased by repeating the algorithm.
And it runs in O((logN)^3) time. So not linear but sublinear unless my math is rustier than i thought.

Re:How to choose?

[techno-vampire]

And it runs in O((logN)^3) time. So not linear but sublinear unless my math is rustier than i thought.

I'm not sure just what you mean by "sublinear," but a few experiments show me that f(x)=ln(x)^3 goes up slightly faster than x does. Could you explain what you mean?

Re:How to choose?

[jfern]

Here's an explination of the running time of Shor's facorization algorithm (which requires a quantum computer). On a flawless quantum computer, it runs in O(N^3) time, where N is the number of digits in the number you're factoring. In reality, with quantum error correction, the running time would probably be O(N^3 * polylog(N)), where polylog(N) is polynomial in log N.

Re:How to choose?

[techno-vampire]

I'm sorry, but that doesn't help. Not only don't you define (or describe) "sublinear," you introduce a new undefined term. I have no idea what "polynomial in log N" could be because you never mention which polynomial you mean. Please define your terms instead of introducing new ones.

A QM foray into the private lives of Alice and Bob

[wwest4]

Alice, instantaneously transfers information about the quantum state of a particle to a receiver called Bob. The uncertainty principle means that Alice cannot know the exact state of her particle. However, another feature of quantum mechanics called "entanglement" means that she can teleport the state to Bob.


Alice: Bob, now that our qubits are entangled, I don't know if mine's spin up down.

Bob: How 'bout I observe yours for you. How about there?

Alice: Nope.

Bob: Here?

Alice: Closer to this side of the gaussian, Bobby.

Bob: How about here?

Alice: OOOOOHHH! You collapsed my wave function DeBroglie!

Bob: Your qubit is now spin up, in case you were wondering... who's DeBroglie?

This...

[Cyno01]

Sounds more like the basis for instantanious comunication (read too much OSC). If we ever invented non reltivistic FTL or spread far enough that we'd need instantanious communication it would probably be based on this.

Re:This...

[QuantumG]

nah, you cant use it for coms, you have to transport the information about the first entangled particle to the second entangled particle using normal communication mechanisms.

Re:This...

[Anonymous Coward]

I don't know if you're a troll or you just didn't RTFA... but here goes...

Entanglment is when 2 (somehow) related particles are psyically separated, yet any quantum change in one results in the same (or opposite) change in the other, with absolutly zero latency...

So, no you don't need to transmit the changing information for the first particle to the second, since they both changed their properties by modifying only one of them...

ok, thats a poor explaination if ever I've seen one... someone wanna lend a hand?

Re:This...

[Anonymous Coward]

Uh, no the point is you can't *choose* which state, so it can't be used for communication. To use the example of two entangled photons, when you measure the spin of one of the photon's, it's either up or down, if it's up then that means the other photon will down and vice versa, but you can't *pick* if it'll be up or down, so it can't be used for FTL communication.

Re:This...

[Mr. Roadkill]

Sounds more like the basis for instantanious comunication (read too much OSC). If we ever invented non reltivistic FTL or spread far enough that we'd need instantanious communication it would probably be based on this.

Actually, even if we never develop FTL transportation, FTL communication could be very, very useful.

Find stars with earth-like planets, send probes containing quantum-entangled data comms gear and pretty well documented interfaces, and invite them to offworld their call centres to India.

Re:This...

[Too Much Noise]

Actually no. There are 2 steps to the process: the 'teleportation' one (collapsing the remote state) and the 'turtle' one (tell the other party what result you measured so that he can rotate his collapsed state to the right one). The second phase is the actual information transmission and it's slower-than-light. Also, you can't skip it by 'guessing', as the possible values for the collapsed state do not even form an orthogonal state[*]. Sorry.

[*] for 2-state particles (simplest case), the measurement of the unknown+transmitter system has 4 possible outcomes, so the receiver can be in one of 4 states in a 2d space => non orthogonal, there's no measurement that will preserve all of them simultaneously, hence there's no knowing whether you destroyed the state or not by only measuring the receiver.

Re:This...

[NonSequor]

Nope, doesn't work that way. In order to make this work you also need a classical (ie slower than light) communication channel. In quantum teleportation, one person interacts a qubit with one half of an entangled pair of qubits, performs a measurement, and then sends that measurement to the other person. The other person then performs an action on their half of the entangled pair that transforms it into the same quantum state as the original qubit. The original qubit is altered in this process and each entangled pair can only be used once.

A lot of people misunderstand the nature of entangled pairs as a result of the fact that many reporters do not understand how they work. An entangled pair is just a pair of qubits set up in a quantum state so that there is a 50% chance they will both be 0 and a 50% chance they will both be 1 (this is an oversimplification, but it's still better than how they are usually explained). If you measure one half of the pair, you automatically know what will happen when you measure the other one.

Not quantum computing, but

[achurch]

Can someone explain why this can't be used for FTL communication? The folks at Cornell seem pretty convinced that FTL communication is impossible, but from my reading of the article, in this experiment the first particle is forced into a known state, so (IANANuclearPhysicist but) it seems to me that if the state of the second particle can be measured (even if that measurement causes the state to change), communication has been accomplished. What am I missing?

Re:Not quantum computing, but

[wwest4]

Because Alice can't know the state of the information she's sending. If she does, then the superposition collapses.

It's not intuitive, but the "collapse of the wave function" metaphor fits observation.

Re:Not quantum computing, but

[jettoblack]

What you're thinking of doing is creating an entangled pair, and keeping one particle on Earth, and keepting the other on a spaceship. Then by changing the state of the Earth particle, you could affect the state of the spaceship particle. Right?

The problem is, we have no way to choose what state the particles will go into when we observe one. Its a random outcome, and you can't acheive any communication if the output is just random noise.

Furthermore, from the spaceship's viewpoint, how do you tell if your particle's state has changed due to an incoming transmission? The only way to know would be to observe it. But, we don't know if that particle had been observed by Earth yet. If it had, then we just disturbed the state that Earth had set. If it hadn't, then we just forced it (and Earth's particle) to a random state. True, the Earth's particle will now be set to the same random value, but random values are still uselss for communication.

For it to work, you'd need a second channel of information, which could transmit some kind of key to decoding the random states into data. Of course, this channel of information would have to go FTL too, so its a Catch-22...

Re:Not quantum computing, but

[jfern]

Quantum teleportation sends a quantum state far away with no physical quantum connection. It can not be used for FTL, because you have to send the other person classical information to tell them what gates to apply to get back the quantum state you started with.

Re:Not quantum computing, but

[Shambhu]

When you look at your particle and collapse it, I don't suppose it is possible to tell if you collapsed it someone at the other end did? Because if you could, you could have a whole bunch of them, look at them at a predetermined time, and then the information would be contained in which particles were already collapsed, not what state they were now in.

But I suspect that, in fact, you cannot tell if the collapse was caused at your end or the other.

Put another way, can you tell when the state changes?

For some reason, this reminds me of the problem of transfering encryption keys over an insecure network. Maybe there is a public-private key analog for quantum communication? ;) A long shot.

Re:Not quantum computing, but

[Anonymous Coward]

The problem is, we have no way to choose what state the particles will go into when we observe one.

Isn't that _exactly_ what a quantum computer does? Seems it computes by influencing [choosing] the state you'll see when you do the measurement.

Re:Not quantum computing, but

[fucksl4shd0t]

It's not that tricky. It's the old "one of us always tells the truth and one of us always lies" riddle.

Two particles, for serial communication. And a flipper ( you know, 1-$var) to tell you which one to read. You only read one at a time, which causes it's state to change to /dev/random. That causes its corresponding earth particle to also change to /dev/random. Then Earth writes to it (we'll call this one A), causing it to change to a known value. So on your spaceship, you read it, and it's a known value (as far as the two particles are concerned).

Earth is also flipping, so now it writes to B. Good, because now you're reading B. And Earth flips again to write to A, and now you're reading A.

Another setup like this gives you full duplex.

Now sprinkle a hundred of them or so into each group, so now you have A and B as groups rather than single particles. All of them are independent, but correspondingly linked to particles on the spaceship. So when you read, if you get some percentage of them being ==, then you know that that is data rather than noise. If you read and they're all different (assuming they will always be different, some threshold can be set) then you know it's noise and to adjust your flipper.

Now, of course, you need to implement TCP/IP over this thing, and you're set.

Re:Not quantum computing, but

[achurch]

What you're thinking of doing is creating an entangled pair, and keeping one particle on Earth, and keepting the other on a spaceship. Then by changing the state of the Earth particle, you could affect the state of the spaceship particle. Right?

Yup, exactly.

The problem is, we have no way to choose what state the particles will go into when we observe one. Its a random outcome, and you can't acheive any communication if the output is just random noise.

But I thought that's exactly what this experiment accomplished. The Physics Web article and diagram certainly suggest that they're teleporting a known state, via the use of a third particle to influence one side of the pair; am I reading them wrong?

Furthermore, from the spaceship's viewpoint, how do you tell if your particle's state has changed due to an incoming transmission?

I'd assume you just repeatedly observe it at fixed intervals to generate a bitstream (or whatever-stream) of incoming information. Even if your clocks shift a bit, you can include periodic timing bits to calibrate--sort of like the Atari 400/800 did with programs recorded on cassette, where stretching of the tape would change the lengths of the recorded bits. This eliminates the need for a subchannel to say "we just made an observation"; just observe all the time and ignore anything that looks like static.

Re:Not quantum computing, but

[AaronLawrence]

From my understanding, you can't write to one particle and have the other follow. All you can do is entangle them, send one off (following the usual rules of the universe), and then LOOK at your "copy". You will both see the same value. It's like you can both look at a light, and see if it is turned on, but neither of you has a light switch. Probably wrong ;)

Re:Not quantum computing, but

[smclean]

I'm not understanding why you couldn't solve the "You would not know if the particle had been observed by Earth yet" by having agreed-upon times by each party in the communication line when particles are read, set and when waits take place.

Earth: Set, Wait, Wait, Read,
Spaceship: Wait, Read, Set, Wait

If each party read the particle's state during one time period, then set the particle to a known value during the next time period, then waited 2 time periods for the other end to do the same, and this action was kept up synchronously, couldn't you transmit information?

Obviously I didn't just blow the lid of quantum mechanics. Is there somewhere I can see a better description of what the 'rules' are beyond 'Reading a particle's state affects the state of the particle'?

Sean

Re:Not quantum computing, but

[jettoblack]

Once you observe either particle of an entangled pair, the entanglement ends and the state is fixed to a single possibility. You can't flip a particle back and forth and still observe changes to its former mate.

Re:Not quantum computing, but

[jettoblack]

But I thought that's exactly what this experiment accomplished. The Physics Web article and diagram certainly suggest that they're teleporting a known state, via the use of a third particle to influence one side of the pair; am I reading them wrong?

IANAQP, but my interpretation of their diagram: Basically, you start with your source particle S and destination particle D. The goal in quantum teleportation is to copy the exact state from S to D. They suggest doing this by creating an entangled pair, A and B. Fire A and S, and B at D. When A collides with S, A's state will be fixed by that interaction, which will instantaneously cause B's state to be changed in the same way, which will impart an identical state onto D when they collide.

The problem is, of course, that A and B have to travel from some half-way point to S and D, and being particles, they cannot travel FTL. So, this method allows us to teleport an exact duplicate of S to D, but not at FTL speeds.

I'd assume you just repeatedly observe it at fixed intervals to generate a bitstream (or whatever-stream) of incoming information.

You can't observe a particle of an entangled pair more than once. After its been observed and their possible states collapse into one definite state, the entanglement stops.

Re:Not quantum computing, but

[Shambhu]

I thought that once you observe it, from either side, the entanglement disappears. Is this correct?

Re:Not quantum computing, but

[the_duke_of_hazzard]

Forgive my naivety, but if Alice can't know the state of the information she's sending, how can that be communication?

Re:Not quantum computing, but

[aXis100]

So...what about if we had a large bucket of pre-entangled particles?

We could take these with us somewhere, then perform the collisions and teleport states, thus communicating a limited amount of data back at FTL speeds.

Now I realise there are current limits on how long entanglement lasts, plus all sort of quantum error correction required, but essentially it *could* be feasible, no?

Re:Not quantum computing, but

[maxwell demon]

Well, what happens is roughly analogous to the following hypothetical "classical teleportation machine":

Alice enters some classical information into an apparatus. That apparatus then generates a random one-time pad, encodes the message and sends the encoded message instantaneously to Bob. Also, it gives the one-time pad to Alice. Now Bob in principle has the message, but he cannot read it (remember: one-time pads are secure; Bob's data is just perfect random data for him). For Bob to read the message, he would have to have the one-time pad. Therefore he cannot get any information before he gets the pad from Alice. But if Alice wanted to transmit that pad instantaneously, she would have to use the teleporter agan, which would then encode it with another one-time pad, making it again useless for Bob until he gets that other pad. So Alice must send that pad to Bob the usual way, which means at maximum with light speed, unless she finds another way to do FTL information transfer.

Re:Not quantum computing, but

[RobertKozak]

I'm not understanding why you couldn't solve the "You would not know if the particle had been observed by Earth yet" by having agreed-upon times by each party in the communication line when particles are read, set and when waits take place.

You are right.
You do not understand. Time is relative.

Re:Not quantum computing, but

[Tremyl]

The trick is a little more subtle than everyone's making it out to be. There is a sort of faster than light transmission here, what Einstein called "spooky action at a distance" (this is the topic of the somewhat famous EPR paper.)

Quantum teleportation is, however, not faster than light. In the case of the simplest way of preforming teleportation, which uses a singlet state, the process is as follows

1) Two particles (photons, atoms, etc) are put into a state with zero angular momentum or its optical equivalent, polarization. 2) One of these particles is shipped from Alice to Bob. They haven't been measured, so they're still in the zero angular momentum state, called a singlet state.

3) Alice takes a new particle, the one she wants to send, and makes a measurement on both it AND her half of the singlet. By measuring both at the same time, she changes the state of both of then, yet does not collapse the wavefunction.

4) This measurement transfers the state of Alice's particle to be teleported onto Bob's particle. Almost. There are four outcomes of Alice's combined measurement, and there are four possible rotations of Bob's particle. In order to recover the state of the original particle, Bob much preform a certain rotation on his oarticle. Without doing this, the state of the particle, when measured, is the same as if no teleportation had taken place.

So, in short, Alice has to send Bob the results of the measurment which teleported the state in the first place, which is slower than (or equal to) the speed of light, or else no information is transmitted.

Re:Not quantum computing, but

[Anonymous Coward]

Surely though if you sent via sub light-speed communications enough data to synchronise the reading of orientation between the two, you could get FTL?

So basically send a sequence for reading the orientation, "horizontal, vertical, vertical, horizontal then repeat" etc.

I know sending the "Key" is not FTL but once the key is in place it could then be used indefinately and achieve FTL comms.

Re:Not quantum computing, but

[Anonymous Coward]

If I put my entagled particles into a space ship with a one time pad. I keep my one time pad and the other half of the entagled particles. My space ship travels 2 light year away at sub-light then sends back pictures instantaneously using the particles and one time pad? Surely this is superluminal communication, I'm getting pictures instantaneously from 2 light years away.

Re:Not quantum computing, but

[maxwell demon]

You misunderstood. The one-time pad is generated on the space ship, exactly at the point of transmission. You don't have a previous one-time pad (of which you could leave a copy at home). While you get the encrypted image instantaneously, you have to wait until the one-time pad to decrypt created at the very same time on the space ship is transmitted back to you.

Re:Not quantum computing, but

[Anonymous Coward]

Surely the one time pad is just an analogy of deciding the orientation to read the particle. It is my understanding there are four. Two horizontal and two vertical (or whatever name you want to assign them). If you read horizontal and the particle is actually vertical you destroy all the information if you read horizontal and it is horizontal you then KNOW if it is up or down. So this is why you need the one time pad. Because if both ship and earth do not align the same you destroy the information. But I don't understand why you cant decide the sequence your going to read the particle before the ship leaves?

Re:Not quantum computing, but

[Tremyl]

No, you have to send what the result of the joint measurement was. The result can't be determined beforehand, so there can't be anything faster than light.

Re:Not quantum computing, but

[Anonymous Coward]

ow ok,

I was under the impression from the article that you could actually decide which spin to make the entagled pair. So I could put it into the exact spin I want. So I can say I want spin X, I do something and therefore know the remote particle is now X, is this not the case?

Re:Not quantum computing, but

[ithicine]

IANAP (I am not a physicist), but it just occurred to me that it might be possible to exploit the simple fact that there *are* state changes every time the particle is observed.

Maybe someone more knowledgeable than me will correct me, but couldn't it be possible to use two particles:

1) a clock pair, jumping to different values at a predetermined rate,
2) a phase pair, jumping values *supposed* to be in sync with the clock pair.

The information is send by choosing when to change the rate of observation of the phase pair, temporarily putting the rate of reception of random values out of sync with the clock pair. Using this scheme, parties A and B could share a "half duplex" communication channel with binary values "in sync" and "not in sync". Of course, we assume both ends have properly working equipment, in constant interaction (but not necessarily communication), thus solving the problem of not knowing if a transmission is being sent.

Possibly overcomplicated and probably wrong, but just an idea... I'd like for someone to point out the problem(s) :)

Re:Not quantum computing, but

[maxwell demon]

No, the one time pad is not about the sequence to read. Indeed, the complete quantum teleportation process actually is about transferring quantum states, that is, including the part which you destroy by directly reading.

The point is that the result of the measurement at the sender side is completely random and therefore independent from the state of the original information to be transmitted. But the measured data gives information of the resulting state. That is, the measurement results in the state being one of four different quantum states at random, and the measurement result on the sender side tells you which of those states it is. And without the measurement result measuring the receiver particles would get random results. Indeed, by measuring them, you cannot even detect if the measurement at the space ship took place.

Thus my analogy with the one-time pad. The teleportation process itself creates the one-time pad at the sender, and at the same time creates the encoded message at the receiver. And only if you have both the encoded message and the code, you can read the message. But since the one-time pad is created (not used as input, but being part of the output) by the process at the sender, you must transmit it to the receiver in order to get the message.

Ok, maybe another analogy helps better. Imagine, you have a transport mechanism to transport a floppy disk instantaneously. However, during the process, the bits on the floppy are changed randomly, so all your data seems to be lost. However, at the sender side, the machine is able to tell you which bits were changed, though not what their previous value was, or what theit current value is. Now, if you transmit that additional information another way, you can then reconstruct the original data, by just again flipping those bits which were changed.

Re:Not quantum computing, but

[king-manic]

You can't observe a particle of an entangled pair more than once. After its been observed and their possible states collapse into one definite state, the entanglement stops.

If you could
a) influence the state of one
b) measure the state of the other

couldn't you just bring a whoel bag of particles and have a communicatiosn channel with a finite lifespan?

Re:Umm...this is old news.

[ioslipstream]

A quick news.google turned up more:

http://news.google.com/news?num=30&hl=en&edition =u s&q=cluster:www%2estartribune%2ecom%2fstories%2f48 4%2f4831579%2ehtml

Need 3 particles

[miyako]

I am not a physicist, or a physics student, or even an arm chair physicist, but from what I understand, creating a quantum gate requires (at least?) 3 particle entanglement, which is quite a bit more difficult than 2 particle enganglement. Can anyone better versed in the subject confirm or refute this?

Re:Need 3 particles

[Smitedogg]

I am not a physicist, or a physics student, or even an arm chair physicist, but from what I understand, creating a quantum gate requires (at least?) 3 particle entanglement, which is quite a bit more difficult than 2 particle enganglement. Can anyone better versed in the subject confirm or refute this?

Disclaimer: I'm a physics student, not a physicist. However, it is my poorly educated thought is that they could use a Fredkin Gate.

Dogg

Re:Need 3 particles

[jfern]

A quantum gate is a unitary matrix (think complex change of basis).
Some gates only require 1 qubit.
For example, the Pauli gates:

X=[0 1]
[1 0]

Y=[0 -i]
[i 0]

Z=[1 0]
[0 -1]

Ultimate Long Distance Communications

[Strenoth]

We hope to be able to use this for computing, but we know it could be used for communication even better. All we have to do is develop better, cheaper tools for manipulating & reading the particals.

Unfortunatly, so far it only seems to work with pairs, we can't seem to get multiples going, so use is limited. but let's try this from the military point of view: In theory, we could build 'ansibles' (to steal from Orson Scott Card) that operate in pairs. Every ship and command unit could have one, the other one would be connected to a complex of normal computers that woudl determine which other ansibles to send the message to.

No static or bad connections, and no need for encryption as there is no way to intercept the communications!

Re:Ultimate Long Distance Communications

[Anonymous Coward]

In theory, we could build 'ansibles' (to steal from Orson Scott Card)

You mean, "steal from Ursula LeGuin"? That's where Card got it from, and he does mention that the name/idea was taken from an old SciFi book in the Ender series.

Re:Ultimate Long Distance Communications

[Xiph]

other than secretely entangling your qubits with theirs (when they're not looking of course)
spies never die, -left out- just get new devices. like a portable qubit entangler.

Re:Ultimate Long Distance Communications

[Kiryat Malachi]

It is currently generally believed that there is no way to manipulate the particles in such a fashion as to allow usable information transfer at a FTL speed.

However, it can be used in conjunction with a classical communication channel to provide uneavesdroppable encryption.

Re:Ultimate Long Distance Communications

[Wilk4]

I wondered how many others would instantly think of Ender's ansible when they read this... ;-)

I'm still confused by this.

[mcc]

Is the idea here basically just that this means that they'll be able to transmit information between qubits without the qubits having to be right next to each other?

Does this mean they might finally break that 7-qubit barrier that quantum computers up until this point had seemed to have been limited to?

I really don't get exactly what's going on. I ASSUME the news doesn't mean that they've find a way to transmit information instantaneously using QE.

Re:I'm still confused by this.

[Medevo]

The point of Quantum Entanglement is that two particles will assume the same quantum state no matter where they are in space. Change one, the other will change, no matter the distance separating them. While the effect is not well understood, it has been demonstrated with photons, and now atoms. This does not directly solve the 7-qubit barrier, but any advancements aren't going to hurt.

If this whole thing of instantaneous communication seems odd, it should. While we are yet to find anything near a economical way to apply QE in communication, it will be coming and lossy communication will be a thing of the past.

Medevo

Re:I'm still confused by this.

[plaa]

Does this mean they might finally break that 7-qubit barrier that quantum computers up until this point had seemed to have been limited to?

There are many ways in which to perform quantum computing. The "7-qubit barrier" probably refers the factorization of 15 using 7 qubits. This was done using NMR-qubits (nuclear magnetic resonance). NMR-computing uses the nuclear spin of atoms in some molecule to represent the qubits. This is relatively easy to achieve, as the atoms are bound close together by the molecule, but it doesn't scale well, because there is a limit to the complexity of the molecule. NMR-qubits are therefore ideal for a proof-of-consept and the research with them is invaluable in the development of quantum computers, but they probably won't have any practical applications. (Of course, it's always possible that some breakthrough comes along...)

The next big thing will probably be trapped ion qubits, where ions trapped with a magnetic and/or electrical field are used to represent the qubits. This allows a much larger number of qubits, but it, too, has its practical limits. There are also other methods (eg. holding particles on a liquid-helium surface), which are not currently practical, but show great potential for the future.

In any development there often seems to be some barriers which cannot be broken, until someone does. This will probably be the case of quantum computers, too.

Re:A QM foray into the private lives of Alice and

[Anonymous Coward]

mod OMFG hilarious

Spooky Action at a Distance

[www.fuckingdie.com]

What happens when quantum computers, which are able to use quantum teleportation, start to exert influence directly over the matter that makes up say a Human Brain for example. Or to make matters worse the brain accidentally starts to exert control over the computer.

"We are sorry - the application you were running has crashed because you were thinking unhappy thoughts."

or

"You have 60 seconds to close and save all thoughts before your brain will be automatically restarted"

Can we say sasser-"cranial edition"

Re:Spooky Action at a Distance

[Anonymous Coward]

Now you're just being silly.

Re:Spooky Action at a Distance

[PsiPsiStar]

Thinking about copyrighted material will violate the DMCA.

Re:Spooky Action at a Distance

[ciroknight]

Technically, it already does.

Re:Spooky Action at a Distance

[mikael]

I thought that everyone knew that if you kept running the compiler on a buggy piece of code enough times, the compiler would eventually become fed up and bored, stop complaining and allow the source code file to compile properly.

Re:Spooky Action at a Distance

[maxwell demon]

Well, actually a large enough quantum computer will inevitably violate somebody's copyright. Just setting up n qubits to have a superposition of states 0 and 1 each, you have a superposition of all states of n bits. If n is large enough, those inevitably will contain bit sequences corresponding to copyrighted data. Even worse: With enough qubits, you'll inevitably have a copy of DeCSS source code in your superposition.

OTOH the RIAA might like other properties of quantum states: It's impossible to copy an arbitrary unknown quantum state. Physically impossible. No way to circumvent it. To make things worse, by even trying, you'll destroy the state.

Sucks to have a DRM scheme built directly into the laws of physics, eh?

Re:Spooky Action at a Distance

[Mikeydude750]

Of course, even listening to the quantum music would result in gibberish...

Then again, I'm sure that's what the RIAA wants in the first place.

Re:Umm...this is old news.

[jfern]

NMR quantum computing techniques have been done a few years ago, but most people think that they don't scale very well. The biggest experiment involved using 7 qubits to find the answer to the age old question: what are the factors of 15?

Stupid 2 minute rule.

Come on CNN, at least try!

[Anonymous Coward]

Did I miss, say an extra page when I RTFA'd? The title is all about how this is an important advance for quantum computing, and yet NO ATTEMPT is made to connect this new entanglement result with quantum computing, unless you count "Teleportation between atoms could someday lie at the heart of powerful quantum computers, which are probably at least a decade away from development, Wineland said. Although his work moved information about atomic characteristics only a tiny fraction of an inch, that's in the ballpark for what would be needed inside a computer, he said."

Maybe somebody can clue me in a little better. Oh, and by the way, I*A*APhysicst.

Electrogravity

[Ceriel Nosforit]

If it is FTL communication, then we've stumbled into the area of electrogravity.
FTL is not an impossibility; it just stands in relation to relativistic physics as it stands in relation to classic physics.

As many know, around a black hole there is a very strong gravitational field. This field has the property of bending the dimension of time itself. We can therefore state that time is not linear, and that a hypothetical theory of electrogravity would be entirely four-dimensional. This would mean that as far as the theory is concerned, there is no difference between cause and effect (as you can from our 3D perspective look at it backwards and forwards; wine filling a shattered glass that reassembles and hops up on the table), and time would be something that only stood in relation to us. The actual EG math, formulas et al., would be like the math familiar from school. - No time variable. - The formulas simply show how things stand in relation to each other, and if one thing is the cause or the other is effect; that is entirely up to us to determine.

Philotics

[natex84]

Is it just me, or does this remind me of the technology behind the ansibles in the Enders series? or maybe i should just RTFA.

Faster Than Light Communication (EPR)

[tal_mud]

This can not be used for faster than light communication. No "information" is exchanged in the "teleportation" it is just that one can "copy" a quantum mechanical state from one place to another, which of course is crucial for building quantum computers. For more explanation on the difference between entangelment and FTL communication see for example see a discussion of the EPR Paradox.

Re:Faster Than Light Communication (EPR)

[wass]

No "information" is exchanged in the "teleportation" it is just that one can "copy" a quantum mechanical state from one place to another

Not quite.

You're correct that quantum teleportation will transfer a quantum wavefunction from one point to another. But it cannot 'copy' the wavefunction. In order to send the wavefunction, the original wavefunction must be destroyed during the process.

Sorry, fanout is strictly prohibited in quantum computing.

Re:Faster Than Light Communication (EPR)

[Anonymous Coward]

I'm over 45 and my brain has started to soften. Can you explain this to me in short, monosylabic sentences? Why, can't this be used for faster than light communication?

Ender's Saga

[g-to-the-o-to-the-g]

For those of you who are interested, there is a series of books called Ender's Saga which explore interesting aspects of advanced physics in a fictional sense. Although I won't go into details (don't want to spoil it), I will say that the books contain very interesting content about a super-being/computer that uses a concept which closely resembles that of entanglment (called philotes in the books). For anyone looking to massage their brain on this subject, give these books a read.

A method to break Quantum Encryption?

[SkiifGeek]

Okay, so this is probably incorrect, but it is a train of thought. With the state of quantum encryption being that if a third party observes the key in transit, it is apparent, and the key is useless, would this have a potential application to break this encryption.

Using this method, the duplicated particles could be observed, leaving the original particles in the encryption stream relatively unmolested. Yes, it would be impractical and the equipment needed would be very distinctive and difficult to hide, but it raises the possibility.

Re:A method to break Quantum Encryption?

[jfern]

Nope, there's a theorem called the no-cloning theorem that says that you can not copy an arbitrary quantum state. There's no way to start with a state |v> and get |v> |v>, which would mean I could perform destructive measurements on one |v> and be left with |v>.

This follows from 2 facts
1. Quantum measurements can be replaced by quantum gates
2. Quantum gates preserve the inner product of two states.

Re:A method to break Quantum Encryption?

[skifreak87]

No because measuring the second entangled prticle has the same affect on the first as directly measuring it. Otherwise one could get around Heisenberg's uncertainty principle which afaik appears to be a law of nature and not something that one can avoid.

Within special relativity, causality can be preserved by forbidding information from travelling faster than the speed of light this does not mean A cannot communicate w/ B FTL but that no useful information to an outside party can be passed (i.e., 1 cannot transmit a bit FTL but could transmit an unknown quantum state one has no control over)

ECC baby

[DigiShaman]

Seriously, ECC correction and redundancy is all that is needed. Even if quantum computers are blistering fast, if getting away with packing 100 individual clusters is available, it will be done. Then, they can all be checked against eachother. Majority rules in a democratic processing fasion.

Re:ECC baby

[jfern]

Quantum codes are more complicated than a simple majority function. The problem is that simple measurement causes the wave function to collapse, which is no good if you're in the middle of a very long computation.

Answers anyone??

[crimson30]

The problem is, we have no way to choose what state the particles will go into when we observe one. Its a random outcome, and you can't acheive any communication if the output is just random noise.

So if we had a consistent way of changing a particles spin back and forth, we would have a method of superluminal communication then?

This is quite good timing, as I was arguing all morning about quantum teleportation (rather coincidental this is, in fact).

My friend was adamant in his stance that you could seperate two particles, change the spin of one and have it oppositely affect the other particle. How this would not lead to FTL communication is beyond me. If you can change the spin of the one particle with a magnetic field, have it change the other over any distance, and figure out the spin without affecting it (as done in 1999 with photons), how would you not have FTL comms?

I assumed his interpretation of quantum teleportation to be wrong... am I wrong here?

Can someone solve our quarrel? Is he right and the only thing stopping FTL comms is they ability to consistently change spin? Or am I right in thinking quantum teleportation is just quantum entanglement over distance (seperate 2 particles, check one and infer the other's spin, nothing more)?

Re:Answers anyone??

[Zaak]

Can someone solve our quarrel? Is he right and the only thing stopping FTL comms is they ability to consistently change spin? Or am I right in thinking quantum teleportation is just quantum entanglement over distance (seperate 2 particles, check one and infer the other's spin, nothing more)?

When two particles are in an entangled state, it means that an observation of one counts as an observation of the other as well. That can be interpreted as information traveling instantaneously from one particle to the other. Lots of people have gotten wacky ideas because of this. However, the information that "travels" between the particles is random, and cannot be used to send information. Bear in mind that it's not the change of spin that is communicated between the two. It's the measurement of the spin, and it only works once, and only if you've managed to maintain the entangled state while you separate the particles.

The unfortunate fact of the matter is that no known phenomenon can be used to transfer information from one place to another faster than light can travel between them. It's not a matter of technical hurdles that must be overcome. It's a matter of fundamental limitations in the way the universe works.

TTFN

Re:Answers anyone??

[Too Much Noise]

1. make the entangled state
   
2. move your particle as far as you like - this is the information carrying process, as you carry the information about the state of the total system
   
3. make a measurement on your particle and 'know' the state of the other - this is just your prior knowledge of the total system; also, note that at this step you disentangled the system, so any further attempts to guess states at the other end are meaningless from either side
   

I want this stuff...

[Anonymous Coward]

Can you imagine playing Unreal Tournament at a ping of 0? and having a Inernetlink with and unlimited speed? [well depends on the put and get on the link ion] You could probably syncronize what ever you want in just a few s.

kindest regards,
mo

Re:I want this stuff...

[DigiShaman]

But what happens if you frag someone before you know it? Oh wait...that would be a good thing ;)

Slashdot a bit slow, news wise...

[Anonymous Coward]

Not to call /. slow, but hell, I heard this on "Paul Harvey's News" around noon-ish yesterday while driving my dad to the doctor's. I mean.... damn.

Re:Communication!

[bussdriver]

forget trying to do computers---figure out how to mass produce it now! bye bye cable modem...cell phone...
"sub-space" communications for the masses.

Thank you Einstein...

[PseudoThink]

For giving the popular press one of the most annoyingly overused quotes ever. PS: spooky first post at a distance.

How do you measure spin?

[Komi]

I know this is slightly off topic, but what physically is spin, and how do you measure it? These experiments always talk about how this property called spin can be entangled with other particles.

IANAP, and in the high level articles I've read, I've never seen spin discussed to anymore depth beyond just that it's a property of fundamental particles. I know that force particles have integer spin (and thus ignore the exclusion principal), and matter particles have half integer spin (and have to obey the exclusion principal), but I don't know what that means physically, or how you measure it. Does it have to do with angular momentum? From a macro world of physics, to measure the angular momentum of something, you can apply a torque and see how quickly it accelerates. I also know that you can measure the charge and mass of a particle by seeing what sort of spiral it makes in a cloud chamber. Is measuring spin related to either of these techniques at all? Thanks for the help!

Komi

Re:How do you measure spin?

[jfern]

The following 3 things are equivalent
A qubit
The spin of an electron
The polarization of a photon

They are equivalent that they can each be representated by a 2 dimensional complex vector, where you don't care about the overall phase (and 0 isn't allowed).

Every played around with polarized lens filters? You have a horizontally polarized lens followed by a vertically polarized lengs, and no light goes through.

You add one that is polarized at 45 degrees, and suddenly 1/8th of your orginal light is going

You can think of your lenses as measuring your qubits (polarization of each of the photons), in different basises, and only letting the ones that were measured as a |0> through.

Re:How do you measure spin?

[ampathee]

I believe that spin is simple a property with no newtonian-physics analog that needed a name. ianap either however :)

Re:How do you measure spin?

[Komi]

Actually now that you mention this, I've seen this analogy before. But that is how you measure the polarization of light. How do you measure the spin of a particle? Is there an equivelent polarized lense for spin? If I want to go to a lab and actually measure the spin of a photon, how do I do that? What tools do I use?

Re:How do you measure spin?

[jfern]

You want the Stern-Gerlach experiment You send the particle through a magnetic field, and then detect it on a photographic plate.

Re:How do you measure spin?

[Anonymous Coward]

Think of a spinning top. It has an angular momentum, and, if it is charged, a magnetic moment too. You could apply a torque (or a magnetic field) to measure it.

Particle spin is a quantum analogy to this, i.e. the electrons etc. behaves as if they where small charged spheres rotating at a fixed speed. (But of course, since we are talking quantum mechanics, this is a too simple picture. You have to take into account the uncertainty principle, quantization (only two states) and all that boring stuff...)

Re:How do you measure spin?

[wass]

Spin is perhaps better explained through it's nomenclature often used by physicists - intrinsic angular momentum

That's basically it. Spin is a kind of angular momentum that just exists in the various particles. Electrons, neutrons, photons, etc all have spin.

Now to get a better idea, you have to understand how angular momentum works in quantum mechanics. Actually, it's quite complicated, and alot of group theory has come around to describe it succintly.

Angular momentum is 'quantized'. A spinning top can spin at any rotational velocity (including two directions - clockwise/counterclockwise). For any given particle, the spin only comes in discrete steps of h-bar, the Plank constant.

The angular momentum must also be centered around 'zero', so this means there are two types of particles. THose with integer spin (having values of -2,-1,0,1,2,etc) or half-integer spin (having values of -3/2, -1/2, 1/2, 3/2, etc). The former are called Bosons and the latter called Fermions. The properties between these two differ vastly (mostly due to QED theory that describes symmetric vs antisymmetric wavefunction upon particle interchange. This gives a 'Pauli-exclusion' law for fermions with no such law for bosons.)

Okay, I don't know if anybody bothered to read this far, but things get more complicated. Each particle has a total spin (photons are spin 1, and electrons are spin 1/2, for instance). But one really doesn't know the 'direction' of the spin, so one can look at the projection of the spin on the z-axis, which has to be quantized. So a spin-1 photon can have a z-projection of -1,0,1. And an electron can be +1/2 or -1/2. If you remember your high-school chemistry and quantum numbers one of them was the spin. This is why each set of n,l,m has two allowed values for the electron spin. But beyond this, one cannot know exactly which direction the spin points because, in quantum mechanics terms, the x, y, and z spin projection operators don't commute. So there's an inherent uncertainty there.

Now to get even more complicated, there's orbital angular momentum (for atoms) and the spin. So this gives the total angular momentum. But adding angular momentum must be done properly within the mathematical confines of group-theory, it's not simple vector-addition at all. So it gets pretty crazy, because you cannot simultaneously know both the total spins z-components of two particles (in specific cases you can, but not in general). So you have things like Clebsch-Gordon coefficients, etc. Anyway, the l and m quantum numbers from chemistry basically come from the orbital angular momentum.

To answer your question about measuring spin, remember it's quantized. But in any interaction the z-component of the spin must be conserved. So if a photon is emitted, that subtracts the total spin by one. So spin of the resulting system must change appropriately (remember the differnece between total spin and z-component of spin). So in a way, torque can be applied by bombarding something w/ particles, but the change in angular momentum must be quantized by units of hbar.

Re:How do you measure spin?

[dido]

Spin is basically an intrinsic angular momentum property possessed by quantum particles. It's as if these particles are all naturally spinning like little tops, and the angular momentum inherent in this spinning is found to always be multiples of 1/2 of Planck's constant divided by twice pi or 1.05450*10^-34 J*s. As you know, the force-carrying particles all have integer spin, and the matter particles all have half-integral spin.

Spin is one of the easiest quantum properties to measure, especially for charged particles, which accounts for its popularity as a building block in quantum computers. You measure spin the same way you measure angular momentum in the macro world of classical physics, apply a torque to the particle. This will cause the particle to precess at a particular rate that would be characteristic of its angular momentum. An easy way to do this for a charged particle would be to place it in a strong magnetic field. A spinning charged particle would have a magnetic moment, hence putting it in a magnetic field would cause it to align with the field, and since accelerating a charged particle causes it to radiate photons, you can measure angular momentum by measuring the frequency of the emitted radiation (this is known as the Larmor frequency). This is essentially what happens in the Stern-Gerlach experiment that first established the quantization of angular momentum (except that the original Stern-Gerlach experiments actually measured the actual physical deflection of ions passing through a nonuniform magnetic field), and is the basis for nuclear magnetic resonance techniques. Some of the most promising quantum computer designs are actually based on using nuclear spins as qubits, and using NMR techniques to prepare spin states and induce the behavior of quantum logic gates.

Ansible Technology?

[crimsonsentinel]

Can you imagine if we could extend this technology to long distances? This sounds freakishly like ansible technology from Ender's Game. I know getting atomic particles to interact in a chain for miles let alone light years will be a challenge, but if this could be done...

Re:Ansible Technology?

[AbsolutCamper]

It can and probably will be done, but not in our lifetimes.

PLLEEAASSEEE!

[Anonymous Coward]

what's the big deal?
imagine cutting a coin in half, so head is on
one piece and tails is on the other piece. now
mail one piece to friend in the us and the other
piece to a friend in asia. once one friend opens
the envelope, he will know instantly(!) what the
other friend received, yes?

Argh!!! NOT teleport, NOT affects.

[elhedran]

Normally I am not so pedantic but the poster repeatedly misrepresented what is happening in entanglement.

4 times in the post it was said that the particles teleport or communicate, they don't.

Its more like the particles are using the same day planner to decide what to do next.

Think of it like to processes running the same code. if they have the same inputs, they will have the same outputs. It doesn't mean they communicate or teleport.

The reason it bugs me so much when people talk as if the particles interact after they have been entangled is it leads someone sooner or later to start asking why we can't use that to beat the speed of light for communication, or a dozen other things that have nothing to do with entanglement.

Re:Argh!!! NOT teleport, NOT affects.

[JTMON]

It has been said by numerous publications that this could be used for teleportation, it's not as if this is the first poster or article to mention or say this. You must know something everyone else is missing

Re:Argh!!! NOT teleport, NOT affects.

[duggy_92127]

The reason it bugs me so much when people talk as if the particles interact after they have been entangled is it leads someone sooner or later to start asking why we can't use that to beat the speed of light for communication, or a dozen other things that have nothing to do with entanglement.

Well, it's not our fault. Even without using words like "teleport", I'm given to understand that after atoms are entangled, when you change the property of one the property of the other changes to match, or opposite. Right? With no apparent delay or physical connection?

So, people like me, when hearing that, think: Okay, so define Property1 as "on" and Property2 as "off". Keep one of the entangled atoms here, put the other on the next Voyager. Voyager communicates with home by twiddling the property of its atom "on" and "off", with the atom here at home mirroring it with no delay, no matter how far away the spacecraft is.

We just don't have enough information to know why that wouldn't work, so getting irked at us isn't helping. I even followed the links and read nothing to debunk the above concept. Would you care to explain why it's bogus?

Doug

Re:Argh!!! NOT teleport, NOT affects.

[p3tersen]

Normally I am not so pedantic but the poster repeatedly misrepresented what is happening in entanglement.
4 times in the post it was said that the particles teleport or communicate, they don't.

The headline on the cover of this weeks Nature reads "Quantum Teleportation with Atoms". What was observed is known in the field as quantum teleportation. While you may dislike this term, the poster was by no means misrepresenting the content of the research.

Re:Argh!!! NOT teleport, NOT affects.

[exp(pi*sqrt(163))]

Look, imagine the world was classical. Then in theory, you could 'teleport' something by measuring every aspect of something, sending the description, and then reconstructing it somewhere else. Strictly speaking this is a true statement but nobody would say "hey, we can teleport stuff now that we have invented the ruler".

Something similar happens in quantum 'teleportation'. Although Heisenberg tells us we can't measure the entire quantum state of a particle we can still transmit the information we need to reconstruct its state somewhere else. (BTW Unlike in the classical case we are forced to mess up the state of the input.) But there's no more reason to see this as a real teleportation then there is to see the ruler as a teleportation device.

Re:Argh!!! NOT teleport, NOT affects.

[Anonymous Coward]

"it was said that the particles teleport or communicate, they don't.

Its more like the particles are using the same day planner to decide what to do next."

WRONG WRONG WRONG

Your problem is you are trying to understand a quantum situation in a way that makes classical sense. START by understanding that the importance of entangement is that it makes NO sense when thought of using common sense or classical physics.

"ACTION at a distance INSTANTAEOUSLY." LITERALLY TRUE. Can't be used to communicate faster than the speed of light in a vacuum. "Teleport" ? Yeah, like quarks have "colors" and "spin". In other words, not like in everyday use; but it is a "term of art" .

Re:Argh!!! NOT teleport, NOT affects.

[hawkfish]

It doesn't mean they communicate or teleport.

Then again, it doesn't mean that they do not communicate.

Re:Argh!!! NOT teleport, NOT affects.

[skifreak87]

Yes and no. If that was the case why would measuring one particle cause the other to collapse into the same wave function? The first one only collapsed b/c it was measured and what it collapses into is random based on some probability distribution determined by the actual value of the quantum state.

Re:Argh!!! NOT teleport, NOT affects.

[Jack Schitt]

>>Think of it like to processes running the same
>>code. if they have the same inputs, they will have
>>the same outputs. It doesn't mean they communicate
>>or teleport.

I don't know about you, but my functions never have predictable outputs.

-The unemployed programmer

Re:Communication!

[Kiryat Malachi]

Except that because you can't control the transition that occurs, you still need a classical communications channel to communicate any actual information. Which is limited by lightspeed.

I love stuff about quantum computing!

[Anonymous Writer]

Too bad I can't bloody understand any of it!

Re:I love stuff about quantum computing!

[Killjoy_NL]

I have the same thing with women :)

Can't be used for communication?

[Anonymous Coward]

People are talking about using this for communication, how are the two particles going to become linked, from the look of things you need the particles in the same area to begin the connection and then you can move them. Is this correct? Please clarify this for some someone.

-Agret

Re:Can't be used for communication?

[maxwell demon]

They must have been in connection at some time to entangle them. But that is before the real communication happens. Imagine we had a way to keep entanglement a very long time, say on a sort of disk. There would be a way to "entangle-format" a pair of disks. Then Alice could send Bob one of the disks in advance, and then, much later, Alice decides to send you a secure message. She puts her disk in the sending device and gives it the original message. Then the sending device does the joint measurement necessary for transmitting the information. This fixes the content of your disk, but to an "encrypted" version of the original message. But the sending device also generates a "decryption key" which is then sent to you the normal way. You then can "decrypt" the data on your disk.

Secondary effects?

[Darkman, Walkin Dude]

Okay IANAQM, but is there no way to check if a particle had changed state, while not in fact observing what that state is? Sort of like seeing light relecting from a surface, and not knowing whether it is from a flashlight or a curtain being pulled back? More observing secondary effects than the effect itself. The type and characteristics of the effect wouldn't be important, merely that there is one. Any one. Like knowing that changes in one particle will cause changes in neighbouring or linked particles, watching them resolve, and leaving the primary quantum link untouched...

If you could do this it would be extremely trivial to set up a communication system that could handle anything digital, from compiling to television transmissions.

Also, as an added bonus, if I get this right, you could also set up a relay to handle near-infinite amounts of different communications simultaneously, limited only by the mechanisms for observing state change...

change in properties of other determinable??

[little_prince]

"Researchers using lab techniques can create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle." ---- Can it always be told beforehand (whether true for all cases) if the other will take identical or opposite properties? Is is controllable/determinable by us what properties the other will take? If A&B entangled and later C entangles with either of them, will it be considered that all three are entangled with each other? and if any property of A changes it will cause some change in properties of B and C to maintain the harmony b/w A,B&C to a state that was? (ought to be?) before the property of A changed? On the wondering scifi side, does all the discussion here, seem to point that parallel universes are possible?? One of the Futurama episodes deals with lots of weird parallel universe stuff (entire universe in a box stuff).

genmay

[Anonymous Coward]

:700k:

Thank you!!

[slubberdegullion]

People need to get this straight. For some hilarious examples of people believing that quantum entanglement can be used for communications, see the scientifically ridiculous movie "The Core" and this slashdot article

This is not good...

[Barkmullz]

Having scientist using words like "spooky" and "weird" cannot be a good thing...

Re:This is not good...

[stor]

"The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' (I found it!) but 'That's funny...'" (Isaac Asimov)

Cheers
Stor

Re:This is not good...

[Anonymous Coward]

do you really think scientists normally use these words? or do you think maybe the journalists use these words to make it sound interesting for non-scientists? maybe if you look at the actual websites of the groups doing the research, or better yet, the actual papers, you would see that they would never use "spooky" or "weird" as these quantum mechanical effects are not that.

Re:This is not good...

[Anonymous Coward]

Your sense of humor just called. It wants to know when you will stop by and pick it up.

quantum bombs?

[nukka]

"Researchers using lab techniques can create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other..."

does this mean that they could create an atomic weapon from a bunch of these atoms all put together? say they make enough of these atoms to make a ball of them that weighed a few pounds, but took one of them and made it split. would this make all of the atoms split at the same time or would the other atoms split at all?

Hate to spoil your fantasies

[jandersen]

Well, actually I don't, but that's another matter.

However, it seems that every time somebody mentions something about 'quantum' people around here go into Batman and Star Trek Mode.

1. This whole thing is still very much in the early days of fundamental research. Think Babbage or Archimedes or something similar. I suspect that much of the hype about 'quantum computing' is simply a magical mantra that produces funding.

2. There still is no such thing as teleportation, not even theoretically. Entaglement only means that you can get two objects to behave 'in step' even at a distance, but so far it has always involved that they start out together, ie. physically close to each other. Teleportation on the other hand is normally thought of as transporting mass from one point of space to another, sort of magically, without passing through the space and time that seperate the two points. There really isn't much chance of that ever making even theoretical sense.

Re:Hate to spoil your fantasies

[Anonymous Coward]

Many people would be satisfied with the ability to fake speed-of-light travel either for inanimate but complex objects (like a computer) or more ambitiously for a living human. Entanglement as I understand it offers some prospects that at least the former would be possible by very quickly "comparing" the component particles of the source to entangled particles, and then sending that information to their counterparts over ordinary radio communications.

You would need to physically send entangled particles between any two sites wishing to use this technology, but even if that had to be done continuously it would be worthwhile for a few very precious and urgent physical deliveries.

This type of teleporter does make some theoretical sense. The information travels at no more than light speed, obeying the laws of physics, it is never sufficient information to know "too much" about any particles for the uncertainty theorem and energy is conserved.

If arbitrarily complex inanimate things can be replicated with this sort of technology then we'd inevitably be tempted to try live things, and if they remained alive as expected, human beings. My guess would be that this would create independent but initially almost indistinguishable people. Their shared experiences would make them different from identical twins, but not so different that society would be unable to cope.

A theoretical Martian colony could in this way be populated with dozens, hundreds or even millions of adult colonists using only local resources and a high bandwidth telecomms bridge back to here. They'd never meet their "originals" because physical travel between the planets is prohibitively expensive.

Sure, it't not Star Trek, but it's a lot different from going anywhere by bus, don't you think?

Re:Hate to spoil your fantasies

[EvilNight]

Well, some folks at IBM have a theory at least.

Not that I know enough about it to make any conclusion myself. The whole thing just sounds suspiciously like Douglas Adam's infinite probability engine to me. :P

Thanks!

[mnemonic_]

This is slashdot. 90% of us (including me) have read those books. Next time RTFC (read the fucking comments), please.

Re:Thanks!

[g-to-the-o-to-the-g]

Rarely does such a great opportunity to karma whore occurr. If you can troll, then I can whore.

THANKS !!! Re:Argh!!! NOT teleport, NOT affects.

[Anonymous Coward]

Now i clearly understand entanglement. But i still don't understand how this can be used to improve quantum computers.

Re: Pipe Dream vs Reality

[Anonymous Coward]

I stand by my prediction that there will never be a quantum computer. It's just a pipe dream of being able to compute all possible combinations simultaneously. It's one of those things that's just not going to happen. Other examples of things that will never happen, no matter how bad we want them:

• Natalie Portman + grits
• Cold fusion
• Time travel
• Warp drive
• Linux on the desktop
• World peace
• SCO execs get jailtime
• Quantum computers
• Teleportation
• Viable "step 2" in the three step business plan

The Improbability Theorem states that all of the above statements can be expressed as "step 1" in the three step business plan. I'll leave the proof as an exercise for the reader.

That means destiny would be a proven fact

[janimal]

Which would lead us to the conclustion that we, indeed, have a destiny which we cannot change... The buddhists would be scientifically proven to be correct, and christians (with the causal evil vs good struggle) to be proven wrong...

Re:That means destiny would be a proven fact

[Ceriel Nosforit]

IIRC this was covered in The Matrix triology, but...
The Heisenberg Principle of Uncertainty in combo with Chaos Theory should be enough to convince anyone that Discordianism is the ultimate One True religion. =)

Spooky Action at a Distance

[errxn]

All I saw was the dame standing there in the glare of the headlights waving her arms like a huge puppet and the code I spit out filled the server and my own buffer.

I wrenched the wheel over, felt the backend start to slide, brought it out with a splash of bandwidth and almost ran up the side of a cliff as the car fishtailed. The brakes bit in, gouging a furrow in the uptime, then jumped to the pavement and held.

Somehow I had managed a sweeping curve around the babe. For a few nanoseconds she had been living on stolen time because instead of getting out of the way she had tried to stay in the stream of the headers. I sat there and let myself stabilize. The butt that had fallen out of my mouth had burned a hole in the leg of my pants and I flipped it out the port. The stink of burned silicon and brake lining hung in the air like smoke and I was thinking of every damn thing I ever wanted to say to a hairbrained MCSE so I could have it ready when I got my hands on her (?).

That was as far as I got.

Anyone else thinking of Orson Scott Cards Ansible?

[Nos9]

If one could entangle a pair of atoms in such a way that it would be relatively easy to change the state of one in a simply meassured way instant communications between any two points in the universe would be possible. You want to talk to Uncle Joe stationed on a Mars expedition? No problem, slap your credit card into the video phone, the telecomms link into NASAs Ansible which links into its partner on the far end, a signal is sent to Uncle Joe that he has a call, and viola you are talking to him.
I just realised that if you could pick and choose multiple diffrent states to measure, say frequency and charge it would make it possible to rely huge amounts of data very quickly, limited only by the speed in which the data can be measured on the recieving end.
The distributed computing possibilities are unbelievable too... The ultimate unbreakable damage proof computer because its parts are scattered across the planet/solar system. No single place would contain a significant amount of the system to allow it to be destroyed without massive effort to get all the pieces worldwide.

Headline

[commodoresloat]

Am I the only one who read the headline and imagined this giant baby walking slowly toward a rack of computers?

Re:Headline

[yecrom2]

Yes.
Yes you were.

A few points.

[slubberdegullion]

1) it is not FTL communication. No information is transmitted.
2) The theory of relativity already takes into account the fact that time can be bent. It is my understanding that general relativity considers the universe as a 4-dimensional space which can be distorted by various effects.
3) time can be nonlinear without being entirely reversible. Causality remains in the theory of relativity, which is well-accepted at this point, even though the theory also incorporates nonlinear time.

Re:A few points.

[Ceriel Nosforit]

Electrogravity renders the normal concept of 'light' a defunct term as it is about combining the idea of the electromagnetic photon with the hypothetical graviton. Most likely it will also do away with the idea of particles in favor of waves as a concept for modelling.
An interesting thing to note here is that particles have actually never been seen, but their existence is assumed because of an interaction that occurs. The idea that only the interaction exists, while the particle is just an idea we invented, seems a bit alien since we are so used to the idea. The possibility that it rests on nothing more than an assumption is disregarded.
A wave as a model is nothing more than that; a model. It is like the 'field' used to describe for instance magnetics. The field is not a real thing itself, but a mathematical model of what interaction to expect where. It is nothing more than a graph in your calculator, without time. Give a value on x, run it through the model, and receive a value one y. Visually you draw the curve, apply the ruler vertically at the x-value, check where it intersects the graph, and read off the y-value. - When you apply this to nature, the x and y is all you see, and the graph is a construct made to predict the future. Both the phenomena and the graph are 'real', but real in quite different ways.

Intermission: I am starting to zone out. Multiple trails of thought, forking out. Attempting not to digress with some difficulty.

A wave-model in this way would only represent the phenomena that can be predicted using it. Nothing would be assumed of what is behind it. The idea of mass could no longer be applied the usual way, as there is no particle to apply it to; only the wave-model of interaction. This puts inertia in a rather new light, and when I figure out how that works, I'm sure I'll reach enlightment.

Sorry if I've only managed being confusing. Standing on the shoulders of giants is much easier than reaching from the ground to the sky. =/

Re:A few points.

[Too Much Noise]

combining the idea of the electromagnetic photon with the hypothetical graviton

'light' is not just the photon. Look at the elevtroweak theory - the photon is the result of breaking the symmetry of a higher-order field. You can in principle add the graviton to this, but to start to observe whether your toy model actually means anything you'd have to go past the symmetry-breaking point in energy. Meaning not in your lifetime, and that's being fairly optimistic.

Most likely it will also do away with the idea of particles in favor of waves as a concept for modelling.

Nonsense. To even observe anything you need interactions, which are particle-like wavefunctin collapses. 'Waves' and 'particles' are eigenstates of operators with incompatible symmetries (aka non-commuting). Unless you do away with the position operator (and hence with space) you're stuck with a valid particle picture; similarly, you'd have to do away with momentum to get rid of the wave picture.

A wave-model in this way would only represent the phenomena that can be predicted using it.

well, duh. Also, bear in mind that mass is still an open question - the Higgs hasn't been positively observed yet.

This puts inertia in a rather new light, and when I figure out how that works, I'm sure I'll reach enlightment.

Inertia can be trivially connected to the wave picture. It means conservation of momentum, which is to say preserving the symmetry of the momentum space (wave picture). To break that symmetry you need an interaction, which in terms of classical physics is represented by a force. Mass should come from the coupling constant for that interaction (the question being understanding the how's). There, are you half-way to enlightnment already?

I'm sticking with Einstien.

[TapeCutter]

Two electrons fly apart from each other at the speed of light. Both have unknown spin ( since we are not allowed to observe them ). Sometime later Jane observes her electrons spin. John now observes the other electron, checks with Jane and finds that Jane's prediction about it's spin is correct (spooky). But how does John know that the state of his electron has actually changed since he was not allowed to observe it before-hand? IANAP but perhaps when the two electrons initially start off as a pair (entangled?) thier proerties are fixed in relation to each other. When Jane observes her electron she will know the proerties of John's before he observes it ( very spooky )!

Re:I'm sticking with Einstien.

[Kiryat Malachi]

You're thinking of something called a 'hidden-variable' theory. They've been (probably) proven to be inaccurate, as far as I can tell - not being a quantum physicist, there's a lot going on that confuses the hell out of me. However, do some googling on hidden variable quantum mechanics if you want to try to understand why this interpretation (initially fixed properties) is considered unlikely.

Re:I'm sticking with Einstien.

[Anonymous Coward]

If you ascribe to the Transactional Interpretation of Quantum Mechanics, based on Feynman's work with EM with half-advanced, half-retarded waves, then the "spooky action at a distance" operates precisely at the speed of light, it's just that it's through an advanced-wave that travels back in time in response to a measurement of one of the particles.

Could be good for interstella comms...

[cheekyboy]

Why cant this TODAY and NOW, be implemented in a digital IO comms box between deep space probs and mars rovers? Then we can have TRUE real time control and transfer of digital data without the need for dishs, or waiting for orbit times etc.... We could get truely amazing real time (or before time) events in view. If its that easy, whats the data rate? can you do this 100000 times a second? 10/second? do you need 10000 atoms?

This would be great for global zero (or 10ms) lag communications around the planet too.

Where are the obvious applications do this?

Also if this is so easy, then RADIO is DEAD!!! this is why no aliens (or future civs from earth) use radio comms, and why radio in space is dead, why cant SETI know this? RADIO is such a crap old invisible tin can communication medium thats had its day, (RIP RADIO 150 years of usage, lets move on)

Re:Could be good for interstella comms...

[Anonymous Coward]

Also if this is so easy, then RADIO is DEAD!!!

... yet for some reason worthy of repeated capitalization... :-)

Somewhat related

[I7D]

Bear with me. This posted is somewhat related to the topic.

If I have a metal pole, and its 100 million miles long, and i'm floating in outer space with it and I give it a good strong push, as hard as I can along its axis, (granted its sheer mass would probably just push my little body backwards) Would the far far end of the pole move as fast as i'm pushing it from the end closest to me?

Also, (and I just thought of this) I've seen tv shows with twins that think similarly, or if one cuts themselves, the other is somehow aware... Creepy as it is, I wonder if there is any instantanious interaction with them, or what laws would govern telepathy?

Anyway, stuff to think about.

Re:Somewhat related

[psmyylie]

Relativistic issues aside, no, the far end would not move right away...it depends on the speed of sound in the metal of your choice. When you push it, you create a pressure wave that is passed along the crystalline structure of the rod as a lattice vibration (a phonon or sound wave if you will), and the other end won't know you're even pushing on it until the phonons have a chance to traverse the length of the rod. As for apparently psychic twins, maybe all twins in the world are just members of a conspiracy that wants to promote the idea of ESP/telepathy, and act accordingly...

Re:Somewhat related

[scorp1us]

Iniertia will hold the top in place until it is acted on by your exertion of force. You can imagine the pole forming a catenary curve, sort of like a parabola. The amount if bend depends on the spring constant of the material. Steel is very elastic and springy (car springs) where as aluminum is not (it just bends).

To see aht it would look like, use a ink tube from a pen trap the top and bottom, and push on it in the center. Over that large distance in your example, all materials that I know of will do the same as the ink tube.

Assuming you got something that was not springy at all, yes the top would move instantly.

The other way to attack it is that you could increase the speed of energy transmittance so that the bowing was instantly fast. Then we are talking about a light beam. The thing is it still won't be stright. Imagine a slinky, stretch it out and put a broom handle in it. then move it to the left. As you move feed more handle into the slinky. The top will stay in place the bottom strightness will increase until the whole slinky is updated to the new angle by the broom handle.

Re:Somewhat related

[exp(pi*sqrt(163))]

This is a troll right? I'm sure the people who repeatedly ask this question on sci.physics are just some evil cabal trying to clog up the discussion.

Anyway, if you push on one end it'd probably take about a year before the other end responded. Mechanical signals travel through steel at around 4,500 m/s, a slong way short of the speed of light.

I've seen tv shows with twins that think similarly, or if one cuts themselves, the other is somehow aware...

Have you every watched Star Trek? In that the characters travel round faster than light. There's a simple explanation for how they do it. Star Trek is fiction.

Quantum Communication ?

[Cpt Kirk]

So ok, I haven't read the whole article and I may not know what I'm talking about :-) but its just an idea..

If you have 4 atoms A,B,Y,Z.
Y and Z are entangled, AND A is entangled with Y and B is entangled with Z
SO if you alter the state of A, Y is affected (which therefore means Z is affected and thus B is affected), if you measure A or B does that collapse the entanglement or whatever or not ?
So do you effectively have communication between Y and Z which is measurable at A and B ???
Was that confusing ? Just a question...

42.

[Dr. Hugh Everett III]

Your quantum computer-based AI starts to spit out messages to the effect of ...

multiverse: (n) an evolutionary quantum computation designed to maximize the probability distribution of happiness across the set of all possible conscious observers.

Quantum Window PCs?

[dcw3]

So does this mean that all the future Windows Quanta PCs will go blue screen at the same time?

I'm kidding...well, sorta.

Re:Quantum Window PCs?

[tr0p]

Just another day in Paradise

Best sig I've ever seen.

Re:Quantum Window PCs?

[Anonymous Coward]

Thanks. It's a tribute to a dearly departed former coworker from fifteen years ago. Someone who always had a smile on his face, and a kind word no matter how grim things appeared to be. This was a man who, on his 50th birthday, rented a bar and dancers (in skimpy attire...this was Korea), and invited all of his friends & coworkers to celebrate...he even flew in his ex-wife!

Spooky...

[unixbugs]

Researchers using lab techniques can create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle.

Does this not scare the living crap out of anyone but me? This is MAGIC.

How come it can't be used for communication ?

[master_p]

Others said that measurement of an entangled particle will make it loose its state (collapse of superposition), but how are we going to get information out of the quantum computer ? can we use the same way to successfully read the quantum state for communication ?

After all, transmission of information in a computer circuit is no different than communication.

Would this analogy work?

[mpn14tech]

I was trying to think in everyday terms why quantum entanglement seems so strange and came up with this. I am not sure if this is accurate so correct me if I am wrong.

It would be like I had two coins that I could flip. Two classical coins could come up as both heads, both tails or one head and the other tails. Normal statistical behavior.

An entangled version of these coins when I flipped them would always come up either both heads or both tails for example. (It could also always be if one is heads, the other must be tails as well)

If this happened with classical coins we would say that something about the coins or environment was rigged. This is what Einstein thought.

However with quantum entangled coins this would be perfectly acceptable behavior.

a classical information channel must be involved

[Anonymous Coward]

Although no information can be transmitted through entanglement alone, it is possible to transmit information using a set of entangled states used in conjunction with a classical information channel. This process is known as quantum teleportation. Despite its name, quantum teleportation can not be used to transmit information faster than light, because a classical information channel is involved.
http://en.wikipedia.org/wiki/Quantum_en tanglement

Voodoo

[Sparky66]

I can't wait for this.. Imagine, once scaled up, this will allow real Voodoo dolls to work! I can't wait to get one, and teleport jabs to my ex-wife.

Help me understand this!

[Anonymous Coward]

I like physics a lot. I have read a lot about string theory. I don't understand all of the mathemtics behind it, but PBS shows have helped me understand the basic nature of it. For a layman, I'd say I have a decent grasp of it.

But this quantum enanglement... It is explained so poorly, I do not understand how it works exactly or it's usefulness!

Here are some questions that have been bugging me:

1. If two particles are entangled, and you measure one... the other one instantly changes it's state. Once you have done this, can you measure either one of them AGAIN and produce another state change in both? Can you keep doing this without re-entangling them?

2. If the answer to 1 is yes, then has anyone found a way to DE-ENTANGLE the particles?

3. What happens if you take a particle that has been entangled with another particle, and try to entangle it with a third? Is this first entangement broken, or do you now have three entangled particles?

4. This is what's really been bugging me...

Let's say you entangle particle A and particle B.

If you cannot measure it without changing it's state, then how do you know that particle B's state changes when you change particle A's state?

In other words...

If have have two boxes... A and B, which have lids on them which are shut, and if I look in box A, and either a rubber duck, or a pineapple appears, how do I know that the contents of box B have changed? I cannot open box B to look at the contents beforehand to know when they change, because that would set the state of box A.

Furthermore...

If I cannot look in box B until after I have looked in box A, then how do I know that box B's contents have changed at all?

How do I know that when my assistant "entangled" box A and box B, that he didn't just go and place a pineapple in both? Since I cannot look in box B beforehand, and I cannot know whether box A does or does not contain a pinapple before I look in it, I have no way of knowing that box A, rather than containing a 50/50 probability of having a pinapple or a duck, does not, in fact just contain a pineapple, and only a pineapple, and box B, which I spent great amounts of money to ship to taiwan, did not in fact always ALSO have a pineapple inside it, because I could not look in it to see if there was a 50/50 state contained inside.

I just do not understand how quantum mechanics could come to the conclusions they have based on what these articles have said about it. It makes no sense. As far as I can tell, if I handed you two boxes and told you that they are entangled, but that if you look in either, it will make the state of both the same, how can you dtermine that that I have not just placed a pineapple in both, and tricked you into thinking you have somehow altered the state of one by looking in the other?

Re:Help me understand this!

[maxwell demon]

1. If two particles are entangled, and you measure one... the other one instantly changes it's state. Once you have done this, can you measure either one of them AGAIN and produce another state change in both? Can you keep doing this without re-entangling them?

No. Once you've measured them, the entanglement is destroyed. Actually, it's not quite right to say you change the state of the one or the other particle, because in an entangled state, the entangled particles do not have a defined state on their own. They only have a joint state, the entangled state. Now measuring them causes that state to "collapse" into one where the particles have a well defined state. However, which state they have is mostly random. The only thing which is fixed is (a) that this state corresponds to whatever you've measured (e.g. if you measured the z-Spin, you'll get a state with defined z-Spin, while if you measured the x-Spin, you'll get a state with defined x-Spin instead), and (b) that the other particle will be in a state which is determined by both the original entangled state and the state the measured particle has after your measurement, even if at the time of the measurement the other particle is lightyears away and has no physical interaction with the measured particle or the measuring device.

So basically, you cannot really change the state of a far-away particle, but you can force a far-away particle which had no well-defined state into one that has, if you have the particle it is entangled with.

2. If the answer to 1 is yes, then has anyone found a way to DE-ENTANGLE the particles?

Should be clear by now: You can detangle them by measuring them.

3. What happens if you take a particle that has been entangled with another particle, and try to entangle it with a third? Is this first entangement broken, or do you now have three entangled particles?

You have three entangled particles.

4. This is what's really been bugging me...

Let's say you entangle particle A and particle B.

If you cannot measure it without changing it's state, then how do you know that particle B's state changes when you change particle A's state?

In other words...

If have have two boxes... A and B, which have lids on them which are shut, and if I look in box A, and either a rubber duck, or a pineapple appears, how do I know that the contents of box B have changed? I cannot open box B to look at the contents beforehand to know when they change, because that would set the state of box A.

Furthermore...

If I cannot look in box B until after I have looked in box A, then how do I know that box B's contents have changed at all?

In other words...

If have have two boxes... A and B, which have lids on them which are shut, and if I look in box A, and either a rubber duck, or a pineapple appears, how do I know that the contents of box B have changed? I cannot open box B to look at the contents beforehand to know when they change, because that would set the state of box A.

Well, that's the complicated one. Does this help you?

Re:Help me understand this!

[pclminion]

If have have two boxes... A and B, which have lids on them which are shut, and if I look in box A, and either a rubber duck, or a pineapple appears, how do I know that the contents of box B have changed? I cannot open box B to look at the contents beforehand to know when they change, because that would set the state of box A.

This is confusing. You talk about things "changing" and looking in the box to see the "contents" beforehand. In the entangled state, the boxes have no "contents" to speak of, only superposed wavefunctions. By observing what is inside the box you collapse both the superposition and the entanglement.

You are asking, how can you know definitively that, before you open one of the boxes, there indeed exists an entangled superposition inside the boxes. You cannot know this. If you open a box to observe the contents, you will never observe a quantum superposition (that would be an absurdity -- it would cause your brain to enter a superposition as well. What the heck would that feel like?), you instead cause the objects to collapse to a well-defined state.

It makes no sense.

Quite right :-) But in some way, it's all connected with consciousness and observation. It seems like our consciousness is always in a well-defined state, and this "rubs off" on whatever we observe, causing any superpositions to collapse. And even if our brains did enter some kind of superposition, would we know it? Would we perceive the superposition, or would we be two superposed people, each observing what he thinks is a well-defined state?

These are questions we probably won't have answers for for a long, long time.

Re:Help me understand this!

[Anonymous Coward]

"But in some way, it's all connected with consciousness"

This was considered a valid theory for decades. It has been DISPROVED by experiment. Conciousness has been proved by experiment to be UNNECESSARY in causing objects to collapse to a well-defined state.

Re:Help me understand this!

[pclminion]

Conciousness has been proved by experiment to be UNNECESSARY in causing objects to collapse to a well-defined state.

I didn't mean to imply otherwise. It is the most obvious and well-known way of causing states to collapse.

Re:A QM foray into the private lives of Alice and

[EReidJ]

A quantum particle is speeding down the road in its car. A policeman pulls the particle over, gets out of his vehicle, and walks over to the quantum particle. The policeman asks:

"Do you have any idea how fast you were going?"

The particle replies,

"No, but I know exactly where I am!"

Ba-dah-bing!

Speed of Quantum Entanglement

[SRain315]

Articles on this subject never specify whether quantum entanglement is limited by the speed of light or not. Has it been tested? Could QE be used for faster-than-light communication?

Weak Measurement

[Dr. Hugh Everett III]

... see also weak measurement as a potential flaw in this argument.

No faster-than-light

[Anonymous Coward]

Unlike what the poster and the article say, the information isn't instantaneously transmitted. Rather, it happens at the speed of light. Past tests involved "teleporting" a photon. But, because it "only" happened at the speed of light, it would've been easier to just let the photon actually go the distance.

Not quite

[gr8_phk]

"whatever happens to one, instantaneously happens to the other."

If one photon hit an object and gets absorbed, the other doesn't spontaneously disappear. If you measure a property of one photon, you can then predict what a measurement of the other photon will be. It's as if they share state information even though theory doesn't allow for it. They say the state is not determined until a "measurement" is made and the wave function "collapses". I'd argue that you can't tell the difference between a particle with a collapsed wave function and one that has not - if you can, then there is spontaneous transmission of information. Let me explain.

I could transmit streams of entagled particle pairs in opposite directions. The transmitting party would either "measure" their photons or not, and the reciever would monitor their stream to see if the photons wave functions are collapsed or not. This would allow faster than light communication.

Truth is, no one really knows what the mechanism of wave function collapse is in detail. Or at least there is no general agreement.

Perhaps I can help ...

[adipocere]

Most people have the following mental metaphor associated with quantum entanglement and FTL data transmission: imagine two people, set roughly a light year apart. By some fun coincidence, their planets are moving in the same direction at the same time. Now, imagine a perfectly rigid rod that runs between the two observers - Alice has an UP arrow on one end and Bob has a DOWN arrow on his. Simply by rotating the rod up and down, the perfectly rigid rod transmits the information instantaneously from one planet to another. Up is now down, down is now up. Have a few of them for control channels ... whammo! FTL data transmission.

Sadly, this is COMPLETELY WRONG.

Instead, Alice and Bob meet on Earth. Alice pulls out a quarter and drops it into this machine. The machine randomly rotates the quarter and then splits it perfectly in half, with the HEAD face rolling one way and the TAIL face rolling the other way. These roll down a little rail into boxes that neither Alice nor Bob can see into.

Bob leaves, with his box via rocketship to a comfy planet off of Sirius. They've calculated all of the relativistic effects of this journey and have their clocks synchronized to account for this. Bob opens his box and finds ... TAILS! Hence, Alice must have the HEAD face.

That is what entanglement looks like, with some fun quantum stuff. Until they opened the box, each box existed in both states, partially, having 1/2 HEAD and 1/2 TAIL probabilities. That's your spooky quantum stuff, right there. Opening the box definitely determines that Alice has the HEAD face when Bob has his TAIL face of the quarter. It has absolutely determined it.

But you can't use that to FTL information about. Whoever opens the box first collapses the wave function. It's over. If Bob has TAILS, he knows Alice has HEADS ... but Alice doesn't know that until Bob calls her on his pitiful sublight telephone system. "Hi, Alice, I have the TAIL face, so you must have the head." Sure, the wave function collapsed all the way across the galaxy, but Alice doesn't know that. Bob has to call her ... on a sublight channel. If he had a superlight channel, then we wouldn't need this nonsense. Catch-22, as someone else mentioned.

And so, quantum entanglement is not useful for this.

Entanglement explained (as I understand it)

[plexxer]

The reason it won't work is this:

Imagine both a sender unit and receiver unit has a random number generator that is linked together somehow to keep them synchronized. It goes along, happily displaying random numbers until a button is pressed. At the time the button is pressed the number it stopped on is displayed at the location at where it was pressed, but since both areas are synchroized, the random numbers stop at the other location - only you don't know because the display only comes on when the button is pushed. So when you push the button and a number is displayed, you don't know if you stopped the random number generator, or if it had been stopped previously and is just displaying the number.

This is sort of how entanglement works (as I understand it). While the two particles can instantly exchange information, the nature of observation makes this information useless.

QC HW questions

[Aumaden]

IANAQP, so...

• What is required to build a QC?
• What equipment do you need to create entangled particles?
• What do you use to measure the state changes?

Are we talking about something that can be realized in semiconductors or are we talking particle accellerators and supercolliders?

Re: Pipe Dream vs Reality

[Sqwubbsy]

When you say 'time travel' do you mean according to Terminator rules, or Back to the Future rules?

Tangling

[TheLink]

What if you consider the entire universe as whole, and that we're all entangled anyway, and "decoherence" is just one sort of entanglement? I mean what really is decoherence and coherence when most stuff was probably tangled from the beginning?

What if they sent one half of pairs of entangled particles on Ship A at near light speed, leaving the corresponding partners on earth. Then you send another bunch on Ship B, 100 years later to meet up with Ship A as it returns half way and you decohere stuff.

Would you be able to figure out when the ships meet by trying to get the different ship's earth bound particles to form interference patterns with each other, pair by pair (in agreed order - a.g. A1 with B1 at Time1, A2 with B2 at Time2).

Hmm, what if part of _you_ were the entangled thing.

Re:Tangling

[maxwell demon]

What if you consider the entire universe as whole, and that we're all entangled anyway, and "decoherence" is just one sort of entanglement? I mean what really is decoherence and coherence when most stuff was probably tangled from the beginning?

There is no "what if". Decoherence is just entanglement with the environment.

What if they sent one half of pairs of entangled particles on Ship A at near light speed, leaving the corresponding partners on earth. Then you send another bunch on Ship B, 100 years later to meet up with Ship A as it returns half way and you decohere stuff.

Would you be able to figure out when the ships meet by trying to get the different ship's earth bound particles to form interference patterns with each other, pair by pair (in agreed order - a.g. A1 with B1 at Time1, A2 with B2 at Time2).

No. Initially you have entangled pairs A/a and B/b (I'm using big letters for the ship particles and small letters for the earth particles). Then when the ships meet and entangle between A and B, you get a four-particle entangled state between A, a, B and b. However, at earth, you only have two of the four particles involved, and therefore you cannot detect that state as entangled, no matter of how many of those states you produce. You always need all parts of the entangled state to get any interference. As soon as one part of the state is missing, you don't get interference. If you can't ever get to that part, you call it decoherence.

Hmm, what if part of _you_ were the entangled thing.

Then you get straight into Everett's Many World Interpretation. According to MWI, then you have a splitting of your worlds (making you observe an apparent "collapse" of the wavefunction).

Re:Tangling

[TheLink]

Thanks. That's cleared things up a bit.

"Everett's Many World Interpretation". Is he the guy that came up with the "I can't be killed MWI"?

I found that funny - it's likely in that scenario that everything would decohere so that the chance of being killed = 100%. But it's obvious I'm no quantum physicist.

Re:Tangling

[maxwell demon]

Well, the MWI is from Everett (though he did himself call it "relative state interpretation"), but the idea of quantum suicide (basically: in your own view you won't die if your death depends on a quantum measurement) is IIRC from Max Tegmark, based on MWI. Quantum immortality is then of course a more or less direct extension. Note however that not everyone who believes the MWI is right also believes quantum suicide works, and also not everyone who believes quantum suicide works also believes the same about quantum immortality.

Re:Tangling

[TheLink]

I think MWI has some good points, but not quantum suicide.

Believing "you won't die if your death depends on a quantum measurement" seems quite farfetched. It could be in the resulting infinite Many Worlds, you are 100% dead, and there's no other possible result.

If you block off BOTH light slits, there ain't gonna be light and dark stripes, it's just going to be pretty dark. You better hope there's a universe where you didn't decide to try blocking off both light slits ;).

IANAQP.

Note that entanglement is just one approach

[exp(pi*sqrt(163))]

Is that so? Care to tell us about the quantum computers that aren't based on entanglement?

Re: Note that entanglement is just one approach

[Scorillo47]

There are many examples, such as the square-root of NOT gate.

Re: Note that entanglement is just one approach

[exp(pi*sqrt(163))]

sqrt(NOT) on its own is uninteresting. Even doing lots of sqrt(NOT) operations on individual qubits is uninteresting and can easily be emulated efficiently in hardware or software today. They only become interesting when you perform them on entangled qubits.

ESP and Quantum Physics.

[ninejaguar]

Researchers using lab techniques can create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle.

In time, they'll probably realize what many throughout the ages have intuited. That the underlying nature of existence (foundations of at least this universe, if there isn't a multiverse) is a single thread, and that if you're skillful and clever you can pluck a note here, and hear it there. It may even be more interesting than that. The underlying reality, or layers of reality like onion skins (some religions consider at least the first layer a form of illusion), may apparently be accessible for manipulation. But, that is only the superficial view by the tinkerers in us.

Philosophical views may be more profound. As scientists start proving that existence isn't an experience shared by many individual minds, but is the byproduct of a single force that doesn't "unite", but cause perceived divisions amongst the sentients for the sake of calculation and experience. Perhaps, answers as to the nature of God could be answered by simply looking in the mirror. It is entirely possible that we are to what we nominally call God, as your fingers are to you. Are God's fingers any less sacred than the rest of God? In the end, being part of something larger, may be taken literally, and that death (the other preoccupying concern, aside from God's existence) isn't actually such an important matter. Particularly, if you die you don't actually go anywhere to be with God, you are simply withdrawn back into God (God being yourself). Except that withdrawn isn't the correct notion either. What are you being withdrawn from? From the rest of reality/God/yourself that represents you/God/reality? No, you may simply metamorph into something else useful/experimental, not standing aloof from your/our/my/God's creation/yourself/God, but changing into another part(no concept of "part" either as everything is One) of creation/yourself.

God/me/you/she/he/it/us may not be intelligent in the form we (humans here) take for granted, but like a general purpose computer/bacteria/amoeba/mother-nature/atoms/physi cs/us that has the ability to build very smart specialized analogs (us, and any alien life forms), in a sense making itself smarter/experienced by growing what it/we/I needs. Not really having a will of its/our own except whatever will we/it/God can give it/God/ourselves. And, arriving at us (sapiens sapiens) isn't an end point. We're/God/I'm all simply part of the experiment/experience/existance called natural-selection/God/existence.

The iterations and failures leading up to us, weren't failures at all, simply different perspectives to our/God's/its experience/growth/search. What are we/God/us/I looking for? An identity? A name? A reason? A purpose? These questions are all simply some of the results of my/our/God's specialized analogs/us in this particular iteration of ourselves/God.

If a 2-Dimensional picture is better than a thousand words, here's a simplification of the ideas I've/we've/God's proposed (and has been proposing to himself/herself/itself/ourselves). The picture is of "La Linea" from a children's television show from the 1980's called "The Great Space Coaster".

La Linea is depicted as an outline or line-drawing of a man, protruding from the ground/universe/existence drawn as a straight line. There is no discernable difference between him and the rest of the universe/everyting-below-the-line, except that instead of being a straight line he has a specific shape. Other than that, the universe/existance and he are one and the sam

Who cares about quantum computers

[Marxist Hacker 42]

Much easier, it seems to me, and much more practical right away, would be the quantum tunneling network card. Bandwidth could be whatever you decide to set the clock speed to- 6 Gbit connections would not be out of the question- for whatever distance you wanted.

The downside, of course, would be that it would only be good for end-to-end; each pair of network cards would only work with the "strange relationship" matched card.

Re:Communication!

[TheLink]

What if you carried a copy of a terabyte of info with you and both parties agree to read off bits at the same time - could that be your classical communications channel?

I'm still fuzzy on this :).

Web Comic Based on QM

[cyb3rllama]

These stories are always interesting to me because I'm an artist working on a web comic that attempts to deal heavily with Quantum Mechanics. If anyone's got the time, I'd appreciate some pointers on making my sci-fi as scientifically tight as possible. The comic is here particlesphere.com. Specific info about the QM aspects can be found on the character and story pages.

Re:Web Comic Based on QM

[Anonymous Coward]

"These stories are always interesting to me because I'm an artist working on a web comic that attempts to deal heavily with Quantum Mechanics. If anyone's got the time, I'd appreciate some pointers on making my sci-fi as scientifically tight as possible. The comic is here particlesphere.com. Specific info about the QM aspects can be found on the character and story pages."

A time capacitor makes as little sense as a left capacitor or blue capacitor or love capacitor.

Forget trying to be "real". Just be interesting. Judged by that, I'd say it looks good so far; keep it up; just forget trying to be "real".

My explanation for why you can't communicate..

[zipwow]

I had this wrong for a long time, and I think I can finally articulate the problem.

What I understand to be really happening is that the particles, when subjected to probability situations, always react the same way.

Imagine you've built two identical big mazes, with several decision points along the way. Ignore any idea of an "end", it's not important.

Now, I've got my quantum entagled rat (particle) and you've got yours. We let them both go in our respective mazes, and after a while, look in to see where they are. No matter how far away we are, both our rats will have made the same decisions all along the way, and will be at the same point in the maze. That's spooky.

But it doesn't communicate anything helpful. If I want to tell you to get some milk, we could agree on some part of the maze as being the "get milk" area. The problem is that as soon as I encourage my quantum-entangled rat to go that way (or otherwise interact with it), I've screwed up the quantum entanglement, and our rats don't behave the same way anymore.

Hope this helps,

-Zipwow

Re:My explanation for why you can't communicate..

[Anonymous Coward]

"What I understand to be really happening is that the particles, when subjected to probability situations, always react the same way."

WRONG WRONG WRONG

Your problem is you are trying to understand a quantum situation in a way that makes classical sense. START by understanding that the importance of entangement is that it makes NO sense when thought of using common sense or classical physics.

"ACTION at a distance INSTANTAEOUSLY." LITERALLY TRUE. Can't be used to communicate faster than the speed of light in a vacuum. "Teleport" ? Yeah, like quarks have "colors" and "spin". In other words, not like in everyday use; but it is a "term of art" .

Re:My explanation for why you can't communicate..

[eluusive]

That isn't exactly correct, it's more like this. There's no "entanglement" at all, as you might think of it.
It's more like this..

Say I have 4 playing cards, each one is an ace. I give you three cards, you have a three out of four chance of having any particular ace contained in your hand. So you look at your cards.

Once you have looked, you also know which one I have. The catch is, none of the cards were any particular ace until you looked at them. Which causes them to become a particular ace. So by looking at your 3 cards, and since there is a limit to what the cards can be, you know what mine is, and caused it to be a a particular ace, without interacting with it.

I could go more in to depth about the ramifications of this, if you want. But I'd rather not type pages and pages right now.

There really isn't any way to convey information this way, only verify that nobody has looked at your cards before you did. Thus quantum "cryptography," which doesn't do any kinds of cipher to the data, it just maintains a secure link, so you don't need to.

whats is the process to 'entagle' particles?

[koa]

Can anyone explain how one goes about actually 'entagling' these particles?

Just curious..

NP Complete Problems

[nate nice]

What effect would a quantom computer have on NP Complete problems and exponential length problems? For instance, could you color a graph every possible way with as few colors as possible (the famous k-colored problem) in one instant?

Entanglement changes everything

[mlg9000]

Entanglement is going to change life on earth as we know it, it's going to happen all at once, and probably within the next 20 years. Besides quantum computers, which give you enough parallel processing power to say; model the human body and test new medical drugs/proceedures/DNA alteration instantly, it also make both wired and wireless a thing of the past. Perhaps you'll still need fiber between quantum nodes (for a backbone) but other then that every networked device could have zero lag, virtually unlimited bandwidth, and access from places like the the bottom of the ocean or mars. Those are realy kind of trivial compared to what could potentially happen; direct communication with the future and past (provided the past is in a time that quantum devices exist). Yo take two identical electrons, place one on a spaceship orbiting some nearby body at high rates of speed, and the other one here on Earth. If you then bring the ship back to Earth you've got two identical electrons with a time gap relative to each other. That might be a new millionths of a second... but that's enough. You can then chain them to together (via multiple electron pairs) and communicate with the future. You might not even need multiple electron pairs... since the people in the future can ask the people in their future the question as so on the answer might just appear. Very cool stuff.

weird quantum world

[Anonymous Coward]

This action at a distance at an instant (NOT AT SPEED OF LIGHT - ACTUALLY INSTANTANEOUS) between two particles when one is acted on is AN EXAMPLE of what the experts are refering to when they say that if quantum physics makes sense to you then you don't understand it.

I personnally make sense of this specific phenomenon by supposing that somehow someway the two particles are at the same point in a curved spacetime by some rules of physics yet to be discovered.

Re:Communication!

[Kiryat Malachi]

Time is relative. So, no.

Re:Communication!

[shaitand]

What if your data is determined not by the current state of transition itself, but rather whether or not a transition has occured?

Transition occured, 1, didn't occur 0

Re:Communication!

[Kiryat Malachi]

You can't/don't know the initial state. If you measure the initial state, you've broken the entanglement.

Re:Maybe Michael will make a smart thread one day.

[GISGEOLOGYGEEK]

Thanks Michael, your attempt to mark me as flamebait for setting your ignorance straight has been noted. ... and the masses continue to laugh at you.

Probability Pollution

[Tablizer]

What if all this new computing pollutes the "probability space" of our universe (or set of parellel universes)?

This may have unforseen results. It is similar to how the dangers of X-rays and radiation were initially ignored and not understood. Who knows what messing with quantum probability space does. We *are* playing dice with the universe(s). We are screwing with poorly-understood forces.

QM is BS

[sillybilly]

Entanglement, mixed states, and parallel universes, they all smell like phlogiston and caloric. Phewww! Yeah they explain a lot of phenomena very "intuitively," just like caloric and phlogiston did. Go read up on those two, then read quantum mechanics and see if you get an eerie, deja-vu feeling. Problem is once your mind is poisoned with a wrong model, it's hard to rid yourself to a clean state. Unfortunately it's hard to describe what's up in QM without abstractly describing the phenomena in it using the language that may already be biased. And how about doing these stupid thought experiements that seldom lead anywhere, because you don't see the surpises that nature throws you. Thought experiments will always give you what you expect, what you think is right, what you think would happen, just like they did with phlogiston and caloric. But only roll your shirt sleeves up kind of measurement means anything, just like with phlogiston and caloric it did, that's where the unexpected shock is that may help you cleanse your head and show, that there, what I've been assuming to be true for ages, that's gotta be wrong.. Unfortunately QM measurements are not as simple as Joule's heat experiments were, with a bucket and a pulley, and most likely, whoever gets do conduct QM experiemtns has an already well poisoned mind because they are a University professor or some other bigshot. But I bet you 5 bux we'll figure all this mess out, just give it time., just like we figured everything out. Just give it time, and watch out for the crazy people, the radical voices. They'll be the Joule of this century. Nevertheless, as far as quantum computing is concered what the real cause for these quantum phenomena is is unimportant, the same rules would still apply, just like the randomness rules still apply to the "deterministic" kinetic gas theory.

I don't want ..

[cfuse]

I don't want a quantum computer as much as a quantum network card.

If the transmission distance is unlimited, I would set up a access point at home (connected to the net) and carry around my quantum networked device.

Even better would be to use this technique to communicate with space probes (ie. Mars rovers). No more waiting for data.

A decade from development?

[Micro$oft $uck$]

Translation: Apple will make it in 5 years, IBM will make it in 10, and Dell will make a half-assed version in 35 years.

Re: rate of collapse

[Anonymous Coward]

It is actually what is done in Quantum experiments. Physicits repeat the operation N times and get statistical results.
I guess in quantum computer, one will have probable results as well.
You will never have 100% sure results, but say 99.99% sure.

Philotes and radiation

[pluggo]

I'm sure some here have read the Ender series... they talk about instant communication through something called an ansible that works on a theory quite similar to what was talked about for wireless quantum communication. It's been a while, but as I remember, two philotes are entangled (or maybe it's one philote is split), and from then on there is a thread of sorts enabling instantaneous communication regardless of distance. If you're interested, there's more information at http://www.philotic.org

If there are particles teleporting around inside my computer, could a bug make particles teleport *outside* the box? What kind of radiation might it create?

One last thing... as I understand it (which I don't really, at least not well :-P), observation changes the state of a particle. Might this serve as a basis for some exploration of the source/seat of consciousness? Does this literally mean that if a living being ascertains the state of a particle that it changes, or is it just that our current methods of making that observation change the observed thing (like light waves bouncing on something)?

Factoring With Shor's

[darkmeridian]

But we are still safe - so far nobody built a working quantum computer that would carry on simple calculations like factorizing the number 15.

This has already been done quite some time ago.

http://www.research.ibm.com/resources/news/20011 21 9_quantum.shtml

Re:Factoring With Shor's

[Scorillo47]

You are right - I meant to say beyond 15... :-)