Quantum Teleportation

Teleportation:

  • A hypothetical method of transportation in which matter or information is dematerialized, usually instantaneously, at one point and recreated at another.
  • Teleportation is the act or process of moving an object or person by psychokinesis. The term originated with Charles Fort, though he used it to describe magical transport between Earth and the heavens.

    Telekinesis is the movement of objects by scientifically inexplicable means, as by the exercise of an occult power.

    Psychokinesis is the production of motion in physical objects by the exercise of psychic or mental powers.

    Quantum Teleportation is the instantaneous transference of properties from one quantum system to another without physical contact.

    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.

    Until recently, teleportation was not taken 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.

    In brief, they found a way to scan out part of the information from an object A, which one wishes to teleport, while causing the remaining, unscanned, part of the information to pass, via the Einstein-Podolsky-Rosen effect, into another object C which has never been in contact with A. Later, by applying to C a treatment depending on the scanned-out information, it is possible to maneuver C into exactly the same state as A was in before it was scanned.

    A itself is no longer in that state, having been thoroughly disrupted by the scanning, so what has been achieved is teleportation, not replication.

    As this figure suggests, the unscanned part of the information is conveyed from A to C by an intermediary object B, which interacts first with C and then with A. What? Can it really be correct to say "first with C and then with A"?

    Surely, in order to convey something from A to C, the delivery vehicle must visit A before C, not the other way around.

    But there is a subtle, unscannable kind of information that, unlike any material cargo, and even unlike ordinary information, can indeed be delivered in such a backward fashion. This subtle kind of information, also called "Einstein-Podolsky-Rosen (EPR) correlation" or "entanglement", has been at least partly understood since the 1930s when it was discussed in a famous paper by Albert Einstein, Boris Podolsky, and Nathan Rosen.

    In the 1960s John Bell showed that a pair of entangled particles, which were once in contact but later move too far apart to interact directly, can exhibit individually random behavior that is too strongly correlated to be explained by classical statistics. Experiments on photons and other particles have repeatedly confirmed these correlations, thereby providing strong evidence for the validity of quantum mechanics, which neatly explains them.

    Another well-known fact about EPR correlations is that they cannot by themselves deliver a meaningful and controllable message. It was thought that their only usefulness was in proving the validity of quantum mechanics. But now it is known that, through the phenomenon of quantum teleportation, they can deliver exactly that part of the information in an object which is too delicate to be scanned out and delivered by conventional methods.

    This figure compares conventional facsimile transmission with quantum teleportation. In conventional facsimile transmission the original is scanned, extracting partial information about it, but remains more or less intact after the scanning process.

    The scanned information is sent to the receiving station, where it is imprinted on some raw material (eg paper) to produce an approximate copy of the original. In quantum teleportation two objects B and C are first brought into contact and then separated.

    Object B is taken to the sending station, while object C is taken to the receiving station. At the sending station object B is scanned together with the original object A which one wishes to teleport, yielding some information and totally disrupting the state of A and B. The scanned information is sent to the receiving station, where it is used to select one of several treatments to be applied to object C, thereby putting C into an exact replica of the former state of A.


    Australian Teleport Breakthrough

    June 17, 2002 - BBC

    It is a long way from Star Trek, but teleportation - the disembodiment of an object in one location and its reconstruction in another - has been successfully carried out in a physics lab in Australia.

    Scientists at the Australian National University (ANU) made a beam of light disappear in one place and reappear in another a short distance away.

    The achievement confirms that in theory teleportation is possible, at least for sub-atomic particles; whether it can be done for larger systems, such as atoms, remains to be seen.

    The more likely applications will come in telecommunications, enabling much faster transfer of data and the use of encryption that can never be broken.

    Teleportation has been one of the hottest topics among physicists working in quantum mechanics - the study of the fundamental structure of matter.

    Some 40 labs around the world are currently trying to teleport a laser beam after pioneering work in 1998 at the California Institute of Technology showed it should be possible.

    'Spooky interaction'

    The Australian researchers have exploited a phenomenon called "quantum entanglement", which links the properties of two photons of light created at the same time. Einstein called it a "spooky interaction".

    What it means is that two photons can be created and sent to different places. It is possible to force one photon into a specific quantum mechanical state and, because the two photons are connected in some way, the other photon will instantaneously take up a complementary state.

    At first sight, entanglement offers the prospect of sending a signal faster than the speed of light. But a closer look at what is actually possible shows that this will not work because of the limits of what can be known about quantum mechanical systems and how such information is relayed.

    But it may offer the prospect of a Star Trek-style transporter.

    Using quantum entanglement, ANU physicist Ping Koy Lam has disassembled laser light at one end of an optical communications system and recreated a replica just a metre away.

    An encoded signal is embedded in an input stream of photons, which is entangled with another beam.

    Elsewhere in the lab, the beam of photons and the associated signal is reconstituted.

    "What we have demonstrated here is that we can take billions of photons, destroy them simultaneously, and then recreate them in another place," Dr Lam says.

    "The applications of teleportation for computers and communications over the next decade are very exciting," he adds.

    Quantum teleportation could make encrypted or coded information 100% secure, Dr Lam said, because even if intercepted the message would be unintelligible unless it was intended for a specific recipient.

    "It should be possible to construct a perfect cryptography system. When two parties want to communicate with one another, we can enable the secrecy of the communication to be absolutely perfect."

    But for a human to be teleported, a machine would have to be built that could pinpoint and analyse the trillions and trillions of atoms that make up the human body.

    Quantum teleporting is problematic for humans because the original is destroyed in the process of creating the replica.

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