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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."
Yet another lazy article submitter copies the article verbatim and gives no credit.
the thing is, faster than light communication would me lots more than just low ping times. it would mean that you could put one end of it in a fast spaceship and then send messages back in time. kids remember: faster than light communication would have way more ramifications than just everquest without lag and talking to mars real quick, you can do lots of things with faster than light communication combined with the fact time isn't absolute.
-You're wasting your time. Alfador only likes me.
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.
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.
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.
My only political goal is to see to it that no political party achieves its goals.
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.
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.
I bet its tons faster than light in super-cold sodium gas. Your statement is meaningless since it has been physicaly demonstrated that light can be slowed,stopped and even made to go FASTER than it normaly travels in a vacuum.
p light.htm
http://science.nasa.gov/headlines/y2002/27mar_sto
If something exists that does not need a creator (god) then why must the cosmos need one?
(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.
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.
make world, not war
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?
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.
Slashdot is proof that Sturgeon's Law applies to mankind.
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.
Very good article, but some people might find Einstein-Podolsky-Rosen paradox article on Wikipedia somewhat better for an introductory text, and at the same time richer in details:
The EPR paradox arises in a thought experiment which shows that quantum mechanics leads to very counter-intuitive and paradoxical consequences. It is named after Einstein, Podolsky, and Rosen, who published the idea in 1935. It is also referred to as the EPRB paradox after Bohm, who converted the idea into something that was nearer to being experimentally testable. The EPR paradox draws attention to a phenomenon predicted by quantum mechanics known as quantum entanglement, in which measurements on spatially separated quantum systems can instantaneously influence one another. As a result, quantum mechanics violates a principle formulated by Einstein, known as the principle of locality or local realism, which states that changes performed on one physical system should have no immediate effect on another spatially separated system. The principle of locality is persuasive, both in intuitive grounds and because it seems at first sight to be a natural outgrowth of the theory of special relativity. According to relativity, information can never be transmitted faster than the speed of light, or causality would be violated. Any theory which violates causality would be deeply unsatisfying, and probably internally inconsistent. However, a detailed analysis of the EPR scenario shows that quantum mechanics violates locality without violating causality, because no information can be transmitted using quantum entanglement. Nevertheless, the principle of locality appeals powerfully to physical intuition, and Einstein, Podolsky and Rosen were unwilling to abandon it. They suggested that quantum mechanics is not a complete theory, just an (admittedly successful) statistical approximation to some yet-undiscovered description of nature. Several such descriptions of quantum mechanics, known as "local hidden variable theories" were proposed. These deterministically assign definite values to all the physical quantities at all times, and explicitly preserve the principle of locality. Of the several objections to the prevailing interpretation of the quantum mechanics spearheaded by Einstein, the EPR paradox was the subtlest. It is at present considered to have been unsuccessful, the existence of hidden variables having been refuted experimentally and the EPR "paradox" taken to be fully resolved within the current interpretation of the theory. The belief that entanglement is a real phenomenon has led to a radical shift in thinking about 'what is reality' and what is a 'state of a physical system'. First, a review of the history: Before 1936, the generally accepted view was that a particle, such as an electron, has measurable properties such as a position and a momentum but 'we cannot know both' at the same time. This view is present in some explanations of the Heisenberg uncertainty principle. In such an explanation, the 'more exactly we measure the position', the 'more we disturb the particle' and its momentum becomes that much less certain. The numerical measure of uncertainty satisfies Heisenberg's principle, but this (local realistic) interpretation is rejected in professional circles, though it still lives in popular books. The shift was caused by the EPR thought experiment, which has shown how to measure the property of a particle, such as a position, without disturbing it. In to
Sincerely,
Pan Tarhei Hosé, PhD.
"Homo sum et cogito ergo odi profanum vulgus et libido."
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.
I haven't seen this mentioned in the threads yet so...
Quantum computing will NOT necessarily speed up all your porn browsing, DOOM playing arses. Instead, Quantum computing affects a set of computational problems that fall into the category of "Non-Determinstic time" algorithms. Non-Determinstic algorithms are identifiable by the fact that they all benefit hugely from being run in parallel. Basically a good rule of thumb is that quantum computing will affect algorithms that gain from being run on massive numbers of processors simultaneously given different (but not inter-communicating) inputs.
Some such problems are:
--Most if not all current cryptography
--SETI
--Other problems where you're looking for one specific output given a potentially huge number of inputs.
As an example in cryptography, a sufficiently powerful quantum computer would be able to break your RSA, DSA, DES3 or any other symmetric or non-symmetric cypher instantaneously if the author of the quantum program knew what they were looking for.
I'm suprised no one has mentioned it so far in the threads...
Karma: The only way to win is not to play.
yes, any observation on a set of entangled particles changes the state of the whole set.
or do you unentangle them before you observe them?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.
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).
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.)
bytesmythe
Hypocrisy is the resin that holds the plywood of society together.
-- Scott Meyer
1.)
Austria != Australia
In Austria there are NO kangaroos, but the Alps, Mozart, Beethoven, Sissy, Schwarzenegger and the river danube in the middle of europe!
2.)
It should not be "Hans J. Briegal of the Australian Academy of Sciences"
but
"Hans J. Briegel of the Austrian Academy of Sciences"
Read more at the University of Innsbruck/Austria page:
http://homepage.uibk.ac.at/homepage/c705/c705114/