Open-Destination Quantum Teleportation

Roland Piquepaille writes "An international team of physicists has entangled five photons for the first time in the world, reports Technology Research News in "Five photons linked." Why is this important? Because it's the minimum number of qubits needed for universal error correction in quantum computing. In other words, they found a way to check computational errors in future quantum computers. The physicists also demonstrated what they call 'open-destination teleportation,' a way to teleport quantum information within and between computers." "They teleported the unknown quantum state of a single photon onto a superposition of three photons. They were then able to read out this teleported state at any one of the three photons by performing a measurement on the other two photons," adds PhysicsWeb in "Entanglement breaks new record ". This will be used in about ten to twenty years to move information among quantum networks. You'll find more details and references in this overview."

Comments

This is what a normal person just read above.

[Anonymous Coward]

Blah Blah Blah Blah,Blah,Blah, You have the bridge #1.

Re:This is what a normal person just read above.

[metlin]

It's actually fairly simple. In QC, you can perform any quantum operations on the qubits, but you cannot look at the bits without losing some information. Therefore, what you do is use error correcting codes, by superimposing the quantum states onto a set of photons whose states you observe, but do not use. What they have done here is basically taken the unknown quantum state of a photon onto a superposition set of three photons, and you can find the state of any one photon by observing the other two photons.

This was predicted a while ago by Alexei Kitaev, and Anton Zeilinger had a preliminary demonstration of a basic q.t. system a while ago. I would imagine that this is just an extension of their works.

Re:This is what a normal person just read above.

[Dorothy 86]

It also means one step closer to computers powerful enough that we can, say for example, model the human body to test all possible drug combinations at the same time.

you forgot that it is one step closer to being able to run Longhorn!

Re:This is what a normal person just read above.

[john_smith_45678]

Thanks Commander Data.

Re:This is what a normal person just read above.

[zangdesign]

One step closer to the singularity...

The day some idiot turns decision making over to computers is the day I start the Butlerian Jihad.

Re:This is what a normal person just read above.

[krumms]

It's actually fairly simple. In QC, you can perform any quantum operations on the qubits, but you cannot look at the bits without losing some information. Therefore, what you do is use error correcting codes, by superimposing the quantum states onto a set of photons whose states you observe, but do not use. What they have done here is basically taken the unknown quantum state of a photon onto a superposition set of three photons, and you can find the state of any one photon by observing the other two photons.

Ah, much better. Thank you for putting it in layman's terms.

Now, if you'll excuse me I think I feel my head exploding ...

Re:This is what a normal person just read above.

[John Courtland]

Maybe this is better: You have a particle. It has a certain and definite state. However, according to Quantum Mechanics, the act of observing the particle changes the state of it. That's no good because you can't rely on that state now. What you do is 'entangle' the particle with other ones, so that they have the same states, and never perform operations on the 'observer' particles. Then you can deduce the state of the 'hidden' particle by the states of the 'observer' ones.

Re:This is what a normal person just read above.

[metlin]

Oh it does. It's just that upon observation, the state collapses and is no longer useful.

It can have any state, in between 0 & 1 -- just that you are not permitted to know what state it is in.

Re:This is what a normal person just read above.

[rufusdufus]

This and its parent are incorrect.

For the parent: the state of all bits become fixed when observation of any member is read; this is simply a noise correction for what is read, a sort of redundance.

For this: this effect does not supply long distance communication. All it does is supply uncrackable encryption. A signal (probably radio) still needs to be sent in order for information to actually be communicated.

Re:This is what a normal person just read above.

[bytesmythe]

Just for the record, the change in one entangled particle does make an immediate effect on the other. They have verified this in laboratory experiments and concluded that the change occurs instantly, not merely at the speed of light.

The problem is this: you cannot actually transfer information using this scheme, only randomness. This is because when you're making the change in the original particle, you cannot control HOW the change is made.

Let's use pennies as an example, pretending that we can "entangle" them like we can subatomic particles so that if two spinning pennies are entangled, if one stops on heads, the other stops on tails, and vice versa. If you take two spinning entangled pennies, then send one of them a few light seconds away, you have a situtation similar to the way these experiments are set up.

So we have these two spinning pennies... Now let's just stop the one still in front of us. Ok, it landed on heads. Now we know the other has just landed on tails. Yet we have not transmitted useful information because we didn't FORCE the penny to land on heads, we just STOPPED the penny. There is no way of controlling how it was going to end up, so all we have transmitted is randomness. This is great for generating randomness for encryption, but you can't communicate with it.

Also, let's set up a different scenario. We'll say that instead of using the states of the tangled pennies to try to transfer information, we'll just use the fact that we stopped them. Now if we have, say, 1000 total entangled pennies (each side having 500), we can agree on a "pennies stoppped per second" rate that is used to transmit information. If we stop 1 penny per second, it's a ZERO bit, and if we stop 2 pennies per second, it's a ONE bit. This means we can transmit a series of 250 ones, or 500 zeroes. But this is instantaneous, so it violates the idea of faster-than-light communication, right?

Actually, it doesn't. However far apart those pennies are when you set up the communications, the "remote half" had to travel at most the speed of light to get there. So, you do not get any increase in the total communication speed.

(You can read more details about quantum entanglement on Wikipedia.)

Re:This is what a normal person just read above.

[elFarto the 2nd]

It can have any state, in between 0 & 1 -- just that you are not permitted to know what state it is in.

Kinda like a women then?

Regards
elFarto

oh please

[OwlofCreamCheese]

oh man... please stop... I dread reading the replys to this story... so so many people not understanding will come up. its not faster than light communication... I promise...

Re:oh please

[Klar]

This could lead to downloading mp3's before they have been recorded.. try to stop that RIAA bastards!

Re:oh please

[britneys 9th husband]

This could lead to downloading mp3's before they have been recorded.. try to stop that RIAA bastards!

I'm going to download mp3s of all of next year's songs, copyright them myself, and release them into the public domain! Bwahaha! Take that, RIAA!

Re:oh please

[tylersoze]

Ugh, you're so right, here we go again. Individual photons, or any massless particle, travel at *exactly* the speed of light, no more, no less. When physicists speak of "slowing down" or "speeding up" light, they are referring to a type of *wave* velocity is which utterly different than the speed of the individual particles making up the wave, is *not* the speed at which information can be transmitted by the wave. There is also no way to transmit information faster than light with entanglement. In fact, in the transactional interpretation (just an "interpretation" mind you, it in no way predicts different effects than other interpreations) the information is transmitted exactly at c, but *back in time* with advanced waves. These are prime examples of complex, subtle subjects that are totally misunderstood by the lay person because of simplified analogies or terminology.

Re:oh please

[Alsee]

Your "understanding" of relativity is wrong. The speed of light is a constant for all observers and this causes all sorts of weirdness in the rest of physics. In particular it it makes it impossible to constistantly define whether two events at different places are "simultaneous". People moving in different directions or at different speeds will see a different order of events. Any method allowing FTL communication can be leveraged into sending a message into someone's past using people moving in oppostite directions fast enough.

Lets say we have a train driving past the earth at half the speed of light, from left to right. We have You standing still on earth with your Magic Instant Communication Device. At the (f)ront of the train we have Fred. At the (b)ack of the train we have Bob. In the exact (m)iddle of the train we have Milly. To make it easy lets assume the train is two light years long.

Now, as the train passes the earth, when it is exactly half way and you and Milly are at the same spot, you signal both Fred and Bob to turn on signalling lights "simultaneously". You will first see both of those signal lights simultaneously one year later, meaning Fred and Bob simultaneously turned them on 1 year ago. From YOUR point of view all is well and good, but that's only because we STARTED from your point of view in the first place.

Now lets look at YOUR view of what happens to MILLY, and then lets look at it from MILLY's point of view.

Milly has moved off to the right at half the speed of light. Fred's light has to pass Milly first, before it reaches you. In particular you'd say it would reach her 8 months after you hit your magic button. Also, by the time you see Bob's light from the back of the train Milly will he a half-light year off to the right. It will take a total of two years for Bob's light to catch up to Milly.

So according to you, Milly sees Fred's signal 16 months before Bob's signal.

Now lets go to Milly's point of view. As far as she is concerned her train isn't moving at all, it's YOU that is flying past at half the speed of light. Fred is motionless relative to her, one light year* in front of her. Bob is motionless relative to her, and one light year behind her. For her the speed of light is still one light year per year and it takes one year for a light to cross either half of the train to reach her. When she sees Fred's signal 8 months after you hit your button she knows Fred had to signal a year before that, or 4 months BEFORE you pressed your button. When she see's Bob's signal two years after you hit your button she knows Bob signaled a year AFTER you pressed your button. Milly can walk up and down the train and measure speeds and distances and all of the laws of physics, and the fact is that for her Fred signaled 16 months before Bob did, not simultaneuosly.

Now lets let Milly reach out and tap your Magic Instant Communication Device while you go zipping past them. She "simultaneously" tells Fred and Bob to turn on their signal lights. Fred's and Bob's signals zip down the train towards her at the speed of light, each singal covers the one-light year length in one year. Milly sees both signals simultaneously. Whoops! Your Magic Instant Communication Device is broken, it does something different depending on who presses the Magic Button.

If we add in a second train travelling in the opposite direction then no matter how you attempt to "fix" your Magic Instant Communication Device there will always be someone somewhere who can send a signal into the past and violate causality. Explaining how and proving it under General Relativity is the stuff of physics papers, not slashdot posts.

Nobody however says that wormholes would violate the laws of temporal causuality.

Flat-out false. Try Google, in particular search on Wormholes and Closed Time-like Loops. A "closed time-like loop" is a path you can fly along to get back to where you strated at the same time (or before) you left. You will find tons of refferen

Very obligatory Futurama

[Anonymous Coward]

They were then able to read out this teleported state at any one of the three photons by performing a measurement on the other two photon

Professor: No fair! You changed the outcome by measuring it!

Already done?

[mozingod]

Open-Destination Teleportation...wasn't this already tested with success? Yea, I seem to remember a story about this. Something about all hell breaking lose and killing all the Marines/scientists that were working on the project though...

Finally...

[PDHoss]

...I empathize with Barbie. Math is hard.

The Wiki-Tome

[RabidChicken]

For those of us who failed High School physics, from Wikipedia: A qubit (quantum + bit; pronounced /kyoobit/ [1] ) is a unit of quantum information. That information is described by state in a 2-level quantum mechanical system.
To be perfectly honest, quantum computing scares me to some extent. Things like PGP encryption and other very sensitive operations could, quite literally overnight, be blown away and dangerously shift power quickly. Then again we will also usher in a new age of unlimited (well, from a 2004 perspective, matter itself ultimately has a limit for storage and processing) computing that can make engineering in all fields like nothing we have seen before. And, the best part, we will see it in our lifetimes.

Re:The Wiki-Tome

[metlin]

And, the best part, we will see it in our lifetimes.

While I appreciate your optimism, I must tell you that the chances of QC taking a giant leap within the next 25 years is quite low.

Sure, people will build preliminary quantum computation elements, and will perform simple operations. But to have a system comparable to existing computers will take a really, really long time.

For one, the resources needed to perform and control such operations is really expensive, and occupy enormous amounts of space. Even technologies used today to achieve the quantum hall effect (one of the primary requirements if you are building a q.c.) is really primitive. For instance, consider MIT's carbon-nanotube technology -- the problem is that while you can achieve q.h.e., not two systems can be duplicated perfectly. Other methods such as building solid state elements to do this (which is what I work on) have been quite unsuccessful.

That, and the fact that we are yet to develop a good enough quantum error correction system. The thing is that in order for QC to take off big time, other areas (material science, nanotech, theoretical CS and information theory, etc) need to progress significantly.

Sure, you may see some primitive QC within the next 40 years or so. But the probability of you seeing a QC capable of, say, solving Primes in P or one that can play you a DVD is quite low. Just my two cents. And yes, IAAQP (I'm a quantum physicist).

Re:The Wiki-Tome

[metlin]

Charles Babbage came up with the concept of the Difference Engine in 1822. It took almost 114 years until Turing to come up with the formalism of computer science, which is the foundation of CS as we know it.

And today, we have half-decent computers - a good 182 years later. Even assuming that the technology is exponential, and the necessary developments in the other areas are made in the next 25 years -- it would atleast be another 34 years after that for QC to take off bigtime and for us to have the equivalet of today's computers (or better) in QC.

I'm not being pessimistic, just being honest about how I feel, as someone who works in this area.

Limited use?

[spellraiser]

From TFA:

In quantum teleportation, complete information about the quantum state of a particle is instantaneously transferred by the sender, who is usually called Alice, to a receiver called Bob.

So, this would only be useful for sending information about a quantum state to guys named Bob? The quantum state thing is limiting enough, but c'mon ... Bob?

Well, tell you what. I'm changing my name to Bob. If you can't beat them, join them. I mean, these guys will be the information uberlords of the future. People will queue up to them, asking 'Did anything come for me yet?' And they will go, like, 'Show me the money!'

The Bobs of the future will be ultra-popular and rich.

...

Yes, I haven't taken my medication today? Why do you ask? :P

Re:Limited use?

[NonSequor]

This is a little tradition borrowed from cryptography. Whenever you describe some apparatus for transmitting information, you refer to the sender as Alice and the receiver as Bob. Other people have added a bunch of other characters, such as Mallory, who represents anyone who might maliciously try to intercept the message in transit.

Re:Limited use?

[Frogbert]

As a person who's name is Mallory I find this comment and your subsequent emails to your girlfriend offensive and arousing respectivily.

Future or syntax?

[sammyo]

"they found a way to check computational errors in future quantum computers."

Just how far in the future will we be able to check? Should be a great aid to debugging! But what happens if I fix a problem that causes my great grandson to come back in time to help me to meet my wife? Oh, wait.

Re:Misunderstanding...

[metlin]

Not in the quantum world. You can transport the data, but you cannot copy the data. This is one of the primary premises of Quantum Computation, covered by the No Cloning Theorem.

Ofcourse, if you are talking about the inherent parallelism in q.c., you are right.

What we don't know

[Anonymous Coward]

What we don't know about quantum physics would float many battleships.

What we may be seeing is the physical evidence that space and time are not much at all like we think they are.

Entanglement seems to allow things far away from each other, that used to be close to each other, to react to each other like they are still close to each other.

Science fiction fans will understand that the most likely explanations for that kind of thing are also likely to be wrong.

I look forward to a better understanding of this kind of behavior because it will allow us to better manipulate and control the way our area of the universe works.

For those who think of this as star trek blek, try putting yourself in the place of someone 200 years ago who was told that someone who lives in England would be able to visit someone in the colonies by a trip of only 3 hours.

dzimmerm (who is at work and whose account does not seem to recognize his password and who does not have any way to pop his home email from work due to SPIT, filtering, and SPIT lotus notes)

Re:What we don't know

[wass]

What we may be seeing is the physical evidence that space and time are not much at all like we think they are.

Actually, this is physical realization of quantum principles that have been known for about 70-80 years. And all of those quantum theories were already verified at the fundamental level. There's no new fundamental physics theory being discovered here, the strangeness of relativistic time/space at the quantum limit (ie, Quantum Field Theory) has been quite well developed and understood for a long time now.

This is more like an applied physics or engineering verification of a quantum applied physicists sketch for quantum error correction of quantum teleportation.

Now if physicsists were able to finally merge gravitation with quantum mechanics, that would be huge and just might float your battleships. But this quantum teleportation is certainly not that at all.

Quantum Teleportation explained.

[Aaron England]

Teleportation is the name given by science fiction writers to the feat of making an object or person disintegrate in one place while a perfect replica appears somewhere else. How this is accomplished is usually not explained in detail, but the general idea seems to be that the original object is scanned in such a way as to extract all the information from it, then this information is transmitted to the receiving location and used to construct the replica, not necessarily from the actual material of the original, but perhaps from atoms of the same kinds, arranged in exactly the same pattern as the original. A teleportation machine would be like a fax machine, except that it would work on 3-dimensional objects as well as documents, it would produce an exact copy rather than an approximate facsimile, and it would destroy the original in the process of scanning it. A few science fiction writers consider teleporters that preserve the original, and the plot gets complicated when the original and teleported versions of the same person meet; but the more common kind of teleporter destroys the original, functioning as a super transportation device, not as a perfect replicator of souls and bodies.

In 1993 an international group of six scientists, including IBM Fellow Charles H. Bennett, confirmed the intuitions of the majority of science fiction writers by showing that perfect teleportation is indeed possible in principle, but only if the original is destroyed. In subsequent years, other scientists have demonstrated teleportation experimentally in a variety of systems, including single photons, coherent light fields, nuclear spins, and trapped ions. Teleportation promises to be quite useful as an information processing primitive, facilitating long range quantum communication (perhaps unltimately leading to a "quantum internet"), and making it much easier to build a working quantum computer. But science fiction fans will be disappointed to learn that no one expects to be able to teleport people or other macroscopic objects in the foreseeable future, for a variety of engineering reasons, even though it would not violate any fundamental law to do so.

In the past, the idea of teleportation was not taken very seriously by scientists, because it was thought to violate the uncertainty principle of quantum mechanics, which forbids any measuring or scanning process from extracting all the information in an atom or other object. According to the uncertainty principle, the more accurately an object is scanned, the more it is disturbed by the scanning process, until one reaches a point where the object's original state has been completely disrupted, still without having extracted enough information to make a perfect replica. This sounds like a solid argument against teleportation: if one cannot extract enough information from an object to make a perfect copy, it would seem that a perfect copy cannot be made. But the six scientists found a way to make an end run around this logic, using a celebrated and paradoxical feature of quantum mechanics known as the Einstein-Podolsky-Rosen effect.

Read just how this effect works, here.

Re:Faster than Light

[metlin]

You are missing something. This has got nothing to do with faster than light communication, instead it's on how they were able to successfully entangle 5 photons, which is the minimum number needed to implement a universal error correction system in quantum computation.

Teleportation was achieved a long time ago by a bunch of folks at Innsbruck, led by Prof Anton Zeilinger.

This is first

[JustOK]

Thanks to quantum computation and teleportation, this is actually the first post.

Re:This is first

[chazzf]

Yes, but the act of modding it up changed its location. Sorry about that...

I don't think three is enough...

[eRacer1]

On my systems three Q*berts is not sufficient for error correction in my simulations. Coily always gets me sooner rather than later.

Re:Misunderstanding...

[metlin]

(Disclaimer: IAAQP)

Yes. They can transmit the data, but they cannot preserve the data without losing information. This is one of the primary ideas behind Quantum Cryptography, which forbids eavesdroppers from creating copies of the transmitted data.

I'm not talking about approximation -- I'm talking of copying the basic qubit as a function of quantum states -- no two quantum states can be copied, and if this were possible it would result in some funny stuff like causality.

You don't have to believe me, see for yourself - No Cloning Theorem.

Re:Quantum...

[karmatic]

In one hour? To quote from the article, "Quantum computers have the potential to be blazingly fast because a string of quantum bits, or qubits, that store the ones and zeros of computer information can represent all the numbers possible within that string at once."

In other words, in the time it takes you to transfer a single porn movie, you can simultaneously transmit _every_ porn movie of the same size or less.

Now that's a lot of porn.

The RIAA Wants Quantum Computing

[serutan]

Quantum teleportation is akin to faxing a document and in the process destroying the original.

[Scene: RIAA Headquarters]
Mitch Bainwol: "This quadrant teleportation thing sounds too good to be true."
Cary Sherman: "Get me Orrin Hatch on the phone. We need mandatory quantum teleplantation by 2010."

Re:Faster than Light

[metlin]

So here's the idea - quantum entanglement is when you have two quantum states that have to be given in reference to each other, even though the two states maybe contained in elements spatially separated.

But - no useful information can be transmitted between the two systems. This is because the information in itself is given by probabilistic superposition of the states. For instance, you have a Qubit defined as the superposition of states, given by |psi> = a|0> + b|1> - so you can only find out when they are absolute states (0) or (1), and not in between -- and that will not happen at speeds less than the speed of light. In order to find out what state the system is in (in between 0&1), you will need to be able to copy the state, which is prohibited by the No Cloning Theorem.

So, to answer your question - you *may* be able to achieve instantaneous transmission of information, but you can never observe that information in a causal fashion less than the speed of light. Did that make sense? :)

Re:But they are entangled!

[qcomp]

If the particles are entangled, and it observe one of the observer ones, isn't that going to change all of them because they are still entangled?

yes, any observation on a set of entangled particles changes the state of the whole set.
However, if you do it appropriately it does change it in such a way, that (a) your measurement tells you nothing about the unknown state and (b) the unknown state is still encoded in the state of the unmeasured particles.

or do you unentangle them before you observe them?

not before - but the act of measurement disentangles the measured particle from the rest. It may lead to *all* particle being disentangled (e.g., if they were in a state |00000>+|11111> and you measure in the basis {|0>,|1>}) or it may leave the unmeasured particles entangled (e.g., if you measure in the basis {|+>=|0>+|1>, |->=|0>-|1>}).

Can you unentangle particles without changing their state?

no, since the state they are in is either entangled or not, disentangling them implies changing their state.
However, the 5-qubit state may be a *redundant* encoding of another state Psi (of fewer qubits). Then it is possible to change the overall state (either by measurements or normal time-evolution) such that one ends up with a single qubit in the state Psi.
This can be useful, since it may allow to if something has happened to the state encoded *without* learning anything about the state. This is the essential idea of quantum error correction: encode in a big (say 2^5-dimensional) space the state of a two-dimensional system. Detect, whether the state has moved out of this subspace (i.e. an error has occurred) but do it such that you do nott distinguish the two states in the subspace (thus leaving it untouched).

Quantum Humor

[ImaLamer]

However, according to Quantum Mechanics, the act of observing the particle changes the state of it.

Werner Heisenberg was pulled over...

Police Officer: Can you tell me how fast you were going?

Heisenberg: No, but I can tell you exactly where I am!