quantum telegraph

One of the weirder bits of quantum theory specifies that atoms or sub-atomic particles can become "entangled." That is, the properties of one depend on the properties of the other; for example, in some kinds of reactions an atom might emit two electrons that spin in different directions. This remains true no matter how far apart they fly. And due to that other famous bit of quantum weirdness, uncertainty, neither electron actually has a spin until somebody measures it. At that moment you "collapse the wave function" of the electron in front of you, forcing it to have one spin state or the other. And simultaneously you force the second electron to take the opposite spin, even if it is a billion light years away.

Ever since this was discovered, scientists and science fiction writers have been wondering how to use the property to create instantaneous communication. We're still a long, long way from the interstellar telegraphs beloved of certain sci-fi writers, but another important if very small step has now been taken:

For the first time, scientists have successfully teleported information between two separate atoms in unconnected enclosures a meter apart – a significant milestone in the global quest for practical quantum information processing.

Teleportation may be nature's most mysterious form of transport: Quantum information, such as the spin of a particle or the polarization of a photon, is transferred from one place to another, without traveling through any physical medium. It has previously been achieved between photons over very large distances, between photons and ensembles of atoms, and between two nearby atoms through the intermediary action of a third. None of those, however, provides a feasible means of holding and managing quantum information over long distances.

Now a team from the Joint Quantum Institute (JQI) at the University of Maryland (UMD) and the University of Michigan has succeeded in teleporting a quantum state directly from one atom to another over a substantial distance. That capability is necessary for workable quantum information systems because they will require memory storage at both the sending and receiving ends of the transmission.

In the Jan. 23 issue of the journal Science, the scientists report that, by using their protocol, atom-to-atom teleported information can be recovered with perfect accuracy about 90% of the time – and that figure can be improved.

"Our system has the potential to form the basis for a large-scale 'quantum repeater' that can network quantum memories over vast distances," says group leader Christopher Monroe of JQI and UMD. "Moreover, our methods can be used in conjunction with quantum bit operations to create a key component needed for quantum computation." A quantum computer could perform certain tasks, such as encryption-related calculations and searches of giant databases, considerably faster than conventional machines. The effort to devise a working model is a matter of intense interest worldwide.