Characteristics of asymmetric superconducting quantum interference devices

Direct current-superconducting quantum interference devices (SQUIDs) charac terized by asymmetric Josephson junctions have never been used for applicat ions. In order to demonstrate their potential advantages, a throughout nume rical analysis of different asymmetric configurations has been carried out. A damping resistance has been included in the SQUID circuit and the therma l noise associated with junction and damping resistances has been considere d in the numerical model. Magnetic modulations and flux noise spectral dens ities have been computed as a function of many parameters (bias current, as ymmetry, SQUID inductance, and damping resistance) and the performance of s ymmetric and asymmetric devices have been compared. The results show that, by properly optimizing the SQUID design, asymmetric SQUIDs are characterize d by higher magnetic flux to voltage transfer coefficient and lower flux no ise. As a result, asymmetric configurations can be very useful in all the a pplications where high sensitivity is required. (C) 2001 American Institute of Physics.