Teleportation Magic, in a Liquid

Scientists have teleported the quantum state of one atomic nucleus to another nucleus. This feat of quantum magic may not be Star Trek, but the researchers not only performed it in a new medium--a liquid--but they were able to confirm that the teleported message had actually been received intact. The technique could one day serve to shuttle information around a quantum computer--a hypothetical device that would drastically speed up calculations by exploiting the ability of quantum systems to be in many states at the same time.

Teleportation relies on a kind of quantum link that can form between two particles: They can be "entangled," so that their quantum states are always complementary and each particle senses what is happening to its partner, no matter how far they are separated. If a measurement on one particle shows that it has an "up" spin, for example, the other particle will have turn out to have a "down" spin, even if it is on the other side of the universe. This quantum channel can be used to teleport the state of a third, "message" particle by entangling it with one of the two original particles and making a measurement on it. The other particle, at the far end of the information channel, will instantly assume the state of the message particle.

Last year, physicists in Austria and Rome managed to teleport single photons, but their experiments left out one crucial step: the final measurement to confirm that the message had indeed been teleported. On 23 October, researchers reported in Science that they had achieved a "complete" teleportation with a stream of photons. But some scientists have suggested that the best medium for a quantum computer might be an organic liquid, where the nuclei could be manipulated with nuclear magnetic resonance (NMR). So Michael Nielsen and his team at the Los Alamos National Laboratory in New Mexico have now teleported information around molecules of the common solvent trichloroethlyene (TCE).

TCE is made up of atoms of hydrogen, carbon, and chlorine. The team nudged the molecules with radio frequency pulses tuned to entangle the spins of a carbon atom (C1) and a hydrogen atom (H). They then entangled a second carbon (C2)--the message particle--with C1. Then came the time for the measurement on C1 and C2, and here the researchers got clever. They simply let the carbon atoms naturally lose touch with each other and assume a definite state, a process identical to making a measurement. Then they measured the final state of the hydrogen nucleus to confirm that teleportation was successful.

But Jeff Kimble, a physicist at Caltech, cautions that teleportation experiments using NMR are notoriously difficult to interpret, because the molecules are a jumbled mixture of different quantum states.

Posted in Physics