Breakthrough in Quantum Teleportation

The teleporter Image credit: Science/AAAS

In this week's issue of Science, physicists working in Japan and Australia reported a breakthrough in quantum teleportation. Using the devise above, known simply as the teleporter, the team, led by Dr. Noriyuki Lee of the University of Tokyo, transported information contained in a beam of light. This is not the first time information has been teleported, the theory of quantum teleportation was devised by American physicist Charles Bennett in 1993 and it was first demonstrated by physicists in Europe and America in 1998. Matter was first teleported in 2009. The results of Lee's team are groundbreaking because no one has teleported such complex information so quickly and accurately before.

Quantum teleportation is similar to classical teleportation. Classical teleportation works by measuring the exact state of an object and then destroying it, only to simultaneously recreate it elsewhere. Quantum mechanics shows that this is not possible because Heisenberg's uncertainty principle states that we cannot measure two non-commuting properties, such as the position and momentum of atoms, simultaneously. Quantum teleportation avoids this problem by sending information in an entangled quantum state.

Quantum mechanics shows that objects can be thought of as being in more than one contradictory state at once. Light, for example, can be thought of as being both a wave and a particle until it is measured. If two objects come into contact whilst in a quantum state then they become entangled.

The term 'entanglement' was coined by Austrian physicist Erwin Schrodinger in 1935. Schrodinger showed that there is no equation that describes the state of a single entangled object and the overall state cannot be equated with any combination of the individual states. Entangled objects remain connected even when separated across vast distances, experiments on one instantaneously effects the other. This is what Einstein referred to as "spooky actions at a distance".

Quantum states are sometimes referred to as 'Schrodinger's cat states'. Schrodinger devised his famous thought experiment in order to criticise the collapse approach to quantum mechanics. The collapse approach, devised by Bohr and Heisenberg, states that only very small objects can exist in quantum states, large objects like people are said to be in classical states. When a quantum state is measured by a classical object, the object is said to 'collapse' the quantum state into a single classical one. Both Schrodinger and Einstein disliked the idea that there should be an arbitrary cut off point at which the laws of quantum mechanics cease to work, especially since there is no explanation for how the quantum and classical worlds can interact at all given that they obey different physical laws.

Schrodinger highlighted these problems by imagining an experiment where a cat is placed in a closed box with a radioactive atom. The atom has a chance of decaying and if it does it will trigger a device which will kill the cat. The collapse approach suggests that quantum states do not collapse until they are measured and so suggests that the cat is both dead and alive at the same time until the experimenter opens the box, thereby measuring the system. The cat itself cannot count as a measuring device. Schrodinger argued that this approach creates a paradox - how can something be both 100% dead and 100% alive at the same time? - and so it cannot be correct. Other approaches to quantum mechanics include Bohmian mechanics and the Everett, or many worlds, approach.

Quantum teleportation works by utilising quantum entanglement. If two objects are entangled and then separated, information can be passed from one to the other. This allows for objects to be teleported as long as the original copy is destroyed. Quantum teleportation does not allow any meaningful information to be sent faster than the speed of light, however, because teleported information cannot be reconstructed without also communicating classically.

Assuming that the mind obeys the same laws of physics as everything else, and you do not accept the collapse approach to quantum mechanics, it is theoretically possible that a human could be teleported. Although it is not known if we will ever be able to do this since the human body is so complex. A lot more work needs to be done before scientists will be able to teleport anything as large as bacteria. Even if humans were able to undergo quantum teleportation, I am not sure that I would want to considering it would involve the complete destruction of my body. The question of whether you could survive quantum teleportation is still a topic of philosophical debate.

Back...