Scheme simplifies quantum chips

Quantum computers promise to solve certain types of very large problems many orders of magnitude faster than today's computers, but coaxing quantum particles like atoms, photons and electrons to carry out computations is no small matter.

Researchers from the University of California at Berkeley and the University of Maryland have brought practical quantum computers a step closer by proposing a type of quantum bit that is relatively easy to build. Qubit's, like ordinary computer bits, represent the 1s and 0s of computer information.

The researchers' architecture sidesteps the previous requirement of extreme precision in the placement of spin qubits -- a tiny area of semiconductor that traps a particle that can represent a 1 or a 0 depending on its spin direction. Spin direction can be pictured as the two possible ways to spin a top -- clockwise or counterclockwise.

The architecture uses electron spin rather than atomic spin, which is more difficult to measure. The qubits in the researchers' scheme are connected through the magnetic interaction between atoms rather than the influence closely positioned electrons have on each other. Ordinarily magnetic interaction would cause every qubit to be permanently connected to every other qubit.

The researchers devised a method to connected and disconnect such qubits. The method allows qubits to be placed further apart than those of previous quantum architectures. This, in turn, allows them to be positioned by ion implantation, an easy-to-use technique that calls for shooting them into the silicon chip with a gun-like device.

It will take at least ten years to build a useful quantum computer device with only a few working qubits, according to the researchers. Many researchers agree that practical quantum computers are two decades away. The work appeared in the November 5, 2004 issue of Physical Review A.