Superconducting qubits show promise

Quantum computing is a goal that both excites and challenges researchers, who are working on a wide variety of physical realizations of the basic building block: the quantum bit, or qubit.

One type is the superconducting qubit made from one or more Josephson junctions. The biggest advantage of superconducting qubits is their strong coupling to microwave signals, which can control the qubits and mediate their interactions. The greatest limitation is their short coherence lifetime.

Despite that limitation, recent experiments have demonstrated the kind of precise control that will be needed to make progress toward a viable quantum computer.

In one experiment, Max Hofheinz, John Martinis , Andrew Cleland and colleagues from the University of California, Santa Barbara, showed that they could impose on a microwave resonator any desired superposition of photon-number states. (M. Hofheinz et al., Nature 459, 546, 2009 .)--Barbara Goss Levi