Big qubits linked over distance

Quantum computers promise to be fantastically fast for solving certain problems, including code breaking that would render today's computer security useless.

The trouble with tapping the traits of particles like atoms and electrons to compute, however, is that they are notoriously difficult to control.

One solution is to bring quantum mechanical behavior into a larger realm.

Researchers from the University of Maryland have moved this approach a step forward by entangling a pair of large quantum bits that were spaced nearly a millimeter apart. Entanglement is a weird quantum property that will allow quantum computers to simultaneously check every possible answer to a problem. Entanglement links a pair of qubits, the building blocks of quantum computers, so that when a logic operation is performed on one, the other changes as well, regardless of the distance between them.

The researchers' prototype entangled qubits were superconducting circuits containing billions of electrons acting as one giant particle. The qubits were 700 microns apart -- a vast expanse by quantum standards, and several hundred times further apart than previous chip-based entanglement experiments.

Researchers generally agree that practical quantum computers are least two decades away. The work appeared in the May 15, 2003 issue of Science.