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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."
Isn't this the correlation effect mentioned in the prime intellect story?
In the PI universe, a Beowulf cluster of these imagines YOU!
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.
This is the first time anyone has been able to use atoms (as opposed to photons) in quantum teleportation.
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?
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
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.
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.
Only the five richest kings of Europe will be able to afford them.
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...
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
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?
ymmv
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...
Don't try to use the force. Do or do not, there is no try.
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.
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).
I doubt, therefore I may be.
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
Don't try to use the force. Do or do not, there is no try.