Flux qubit in a dc SQUID with the 4π period Josephson effect

¹ School of Physics and Engineering, Sun Yat-sen University - Guangzhou 510275, China
² Department of Physics, Shaoxing University - Shaoxing 312000, China

^(a) yaodaox@mail.sysu.edu.cn
^(b) wangzh356@mail.sysu.edu.cn

Received: 31 January 2015
Accepted: 4 May 2015

Abstract

We propose a superconducting flux qubit in a dc SQUID structure, formed by a conventional insulator Josephson junction and a topological nanowire Josephson junction with Majorana bound states. The zero-energy Majorana bound states transport 4π period Josephson currents in the nanowire junction. The interplay between this 4π period Josephson effect and the convectional 2π period Josephson effect in the insulator junction induces a double-well potential energy landscape in the SQUID. As a result, the two lowest-energy levels of the SQUID are isolated from the other levels. These two levels show counterpropagating supercurrents, thus can be used as a flux qubit. We reveal that this flux qubit has the merits of stability to external noises, tolerance to the deviation of system parameters, and scalability to large numbers. Furthermore, we demonstrate how to couple this flux qubit with the Majorana qubit by tuning the junction parameters, and how to use this coupling to manipulate the Majorana qubit.