QUANTUM TELEPORTATION

"Beam me up" is one of the most famous catchphrases from the "Star Trek" series. It’s the command issued when a character wishes to teleport from a remote location back to the Starship Enterprise. While human teleportation currently exists only in science fiction, teleportation is possible now in the subatomic world of quantum mechanics - not in the way typically depicted on TV. In the quantum world, teleportation involves the transportation of information, rather than the transportation of matter.



Research is an important step in improving quantum computing, the scientists say and has the potential to revolutionize technology, medicine and science by providing faster and more efficient processors and sensors.


Quantum teleportation is a demonstration of what Albert Einstein famously called "spooky action at a distance" -- also known as quantum entanglement. In entanglement, one of the basic concepts of quantum physics, the properties of one particle affect the properties of another, even when the particles are separated by a large distance.


We can debate whether ‘quantum teleportation as a term is a catchy way of conveying a scientific idea, or a misleading bit of hype. But the real question — what, exactly, is transmitted during quantum teleportation, and how — touches on issues much more profound.


Whatever it’s called, the process transfers the quantum state of one particle onto another, identical particle, and at the same time erases the state in the original. This situation can’t be meaningfully distinguished from one in which the original article itself has been moved to the target location: that transport has not really happened, but to all appearances, it might as well have.




Crucially, however, this works even if you do not know what ‘information’ you are sending — that is, what the quantum state of the original particle actually is. That's important because making a measurement on an unknown quantum signal can disturb and alter it.

Teleportation of a quantum state uses the phenomenon of quantum entanglement as a means of transmission. When two or more particles are entangled, their quantum states are interdependent, no matter how far apart they are. In effect, they act as a single quantum object, described by a single wavefunction — the mathematical construct that encodes all the quantum properties of the object.


The procedure begins by entangling a pair of particles to set up the quantum transmission channel. Particle A is held by the sender and B is sent to the receiver. Because the particles are entangled and thus interdependent, if A performs a physical operation on hers, that can be instantaneously reflected in the state of B.


A common view is that quantum teleportation is a new way of transmitting information: a kind of high-speed quantum Wi-Fi. What’s amazing about it is that the quantum 'information' is ‘sent’ instantaneously — faster than light — because that is how two entangled particles communicate.


But isn't that supposed to be forbidden by Albert Einstein’s special theory of relativity? Yes — and that problem lay at the root of Einstein’s objections to the standard interpretation of what quantum entanglement entailed (he dubbed it “spooky action at a distance”).

What special relativity actually prohibits is faster-than-light causal influence: an event in one place can’t have a physical, observable effect at another place in less time than it takes for light to travel between the sites. Quantum teleportation does not transmit any faster-than-light causal influence, because you also need the classical channel — limited to light speed at best — to complete the process.



It’s crucial that the teleported state is never actually copied. The fact that it is destroyed during the entanglement-enabled teleportation ensures that there is never a duplicate. The process thereby observes a fundamental principle in quantum mechanics, called no-cloning: it is impossible to make a copy of an arbitrary (unknown) quantum state5.

That prohibition causes problems related to handling errors in quantum computing but also enables the technology called quantum cryptography, which makes it impossible to eavesdrop on a message encoded in quantum states without being detected6.

No-cloning is more than a technical complication of quantum information technology. Some researchers suspect that rather than being a consequence of the rules of quantum mechanics, it is in fact one of the deep principles — almost a fundamental axiom — that result in counter-intuitive quantum phenomena such as entanglement in the first place.




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