Characterization of double-loop four-Josephson-junction flux qubit

• Published in: Physica. C, Superconductivity Vol. 469; no. 15; pp. 1608 - 1611
• Main Authors: Shimazu, Y., Saito, Y., Wada, Z.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2009; Elsevier
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; DC-SQUID; Electronics; Exact sciences and technology; Flux qubit; Josephson junction; Physics; Proximity effects, weak links, tunneling phenomena, and josephson effects, adreev effect, sn and sns junctions; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Superconducting devices; Superconductivity; Flux qubit; 85.25.Am; 85.25.Dq; Josephson junction; 74.50.+r; DC-SQUID; Magnetic flux; Quantum interference phenomena; Quantum bit; Energy gap; Asymmetry; Josephson effect; Double well model
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2009.05.213

An advantage of a double-loop four-Josephson-junction (4-JJ) flux qubit is the tunability of the energy gap at a symmetry point, i.e., the point at which the double-well potential of the qubit is symmetric. The energy gap is controlled via the magnetic flux in a DC superconducting quantum interference device (DC-SQUID) loop incorporated in a 4-JJ qubit. We investigate the locus of the symmetry point in the plane of two control fluxes of the qubit, taking into account the asymmetry in the DC-SQUID, which is inevitable in practical cases. The observed positions of the qubit steps are in reasonable agreement with the calculated locus of the symmetry point. We estimate the asymmetry parameter of the DC-SQUID from this analysis.