Unconventional Josephson Junction Arrays for Qubit Devices

Abstract

The presence of spontaneous currents in unconventional Josephson junctions gives rise to the possibility of using zero magnetic field magnetization states in an unconventional loop as qubit states in a Josephson quantum computing device. However, the advantage of zero field may be insufficient to overcome the problems arising in the design and fabrication of low-noise, low-dissipation, reproducible devices. On the other hand, low-T/sub c/ "flux" devices suffer the same problems though their perspectives are more promising. The solution could be an increase in the device complexity, but with the gain of an effective advantage on the external noise rejection of the system during quantum evolution. Using advanced fabrication techniques it is now possible to build Josephson junction arrays made of superconducting unconventional loops. On this basis, a new qubit device can be designed as a ring array of unconventional loops. From a theoretical point of view this device is analogous to an annular Josephson junction, but with a "built in" natural degeneracy. For their topological and energetical properties, such arrays could be excellent devices for the qubit circuitry usable as the basic building blocks for quantum computing devices. In this work, we show how some of the principles of qubit design could be implemented in such devices.