Vastly powerful quantum computers are still many years away, but researchers have filled a major gap in the tools needed to construct them. Two groups have recreated the quantum state of one atom in a distant atom for the first time. Researchers already did this with photons (ScienceNOW, 10 December 1997) and atomic nuclei (ScienceNOW, 4 November 1998) some time ago, but atoms are more promising memory elements for future quantum computers.
Such devices would take advantage of superposition--atoms' weird quantum ability to be in two states at once. Multiple atoms combining states could rapidly perform calculations that would take years to crunch on a conventional computer. For that to happen, though, atoms on one side of the computer would have to be able to tell atoms on the other side what they've just been doing. For example, atom A might "teleport" its superposition of spin states (or some other property) to atom C. One scenario for doing this involves an intermediary atom, B, that is entangled with C, meaning the pair's spins are intertwined, no matter how far apart they are. Because of this entanglement, measuring the relative orientation of A's and B's spins reveals how A's and C's spins are related too and how to manipulate C to make them identical, thereby teleporting A's superposition of spin states to C.
Two groups have now done just that by trapping a row of atoms in an electric field and tweaking them with lasers, they report in the 17 June Nature. Both teams learned over the past year how to manipulate and measure quantum states in groups of three charged atoms or ions. Now, Rainer Blatt of the University of Innsbruck in Austria and colleagues have teleported the superposition of electronic states from one calcium ion to another. The secret was keeping the ions relatively far apart, which made it easy to change the state of each one individually with a tightly focused laser.
The other approach, pioneered by a group from the National Institute of Standards and Technology in Boulder, Colorado, used beryllium ions caught in a trap with multiple wells for holding ions. They shuffled the ions from one spot to another and hit them with three lasers to teleport the superposition of vibrational states from one ion to another. Keeping the ions cold was the key to reliably shuffling them, says group leader David Wineland.
"It's another step closer to a quantum computer, although that is still pretty far away," says Steven van Enk of Bell Labs in Murray Hill, New Jersey. "The methods were really different. That's very promising," he says, because if one technique proves difficult, researchers will have a fallback.