Development of a Superconducting Differential Double Contour Interferometer.

We study operation of a new device, the superconducting differential double contour interferometer (DDCI), in the application for the ultrasensitive detection of magnetic flux and for digital read out of the state of the superconducting flux qubit. DDCI consists of two superconducting contours weakly coupled by Josephson junctions. In such a device a change of the critical current, caused by an external magnetic flux or a nearby electric current, happens in a step-like manner when the angular momentum quantum number changes by one in one of the two contours. With a choice of parameters, the DDCI may outperform traditional superconducting quantum interference devices.