[main] [publications] [data] [phonelist] [group stuff]

Quantum Computer built on Superconductors

Quantum Computer (QC) exploits the property of quantum mechanical system to be in a superposition of several distinct states. In such system information can be stored in quantum state F=a|0>+b|1> as opposed to 0 and 1 - only states allowed for classical computer.

One doubly-degenerate two-level quantum system required for QC operation is the superconducting loop with a Josephson junction in it, or rf-SQUID (Leggett, 1983). In such circuit two states are the directions of current flow in the loop. Recently it was shown (Friedman, 2000) that these two states can be made coherent, i.e. current can flow in both directions simultaneously, which is not allowed by classical physics.

The important element for stability and environmental decoupling of the superconducting QC is the pi-junction (Josephson junction with pi phase drop across it). The first pi phase shifting device was built in the DVH group in 1993 on the base of YBCO d-wave material. Currently we are working on other types of pi-juncions: mesoscopic quasiparticle injection SNS junction and SFS junction.

For more information:

Yuriy Makhlin, Gerd Schoen, Alexander Shnirman, Quantum state engineering with Josephson-junction devices