Superconducting Quantum Interference Filters Operated in Commercial Miniature Cryocoolers

Abstract

Superconducting Quantum Interference Filters (SQIF's) are multi-loop arrays of Josephson junctions possessing unconventional grating structures. The flux-to-voltage transfer function of SQIF's is unique and has a single delta-peak like characteristics at zero applied magnetic field. The fault tolerance of SQIF's allows them to be realized in standard high-temperature grain boundary Josephson junction technology. We have successfully designed high-temperature YBCO SQIF's with voltage swings of more than 3 mV and a rather large dynamical range. This large dynamical range allows high-Tc SQIF's to be operated in commercial miniature cryocoolers at 50 K-80 K without any significant problems. Typical parasitic oscillations which are induced by the 55 Hz driven compressor of the cryocooler do not degrade the performance of SQIF's. Even if SQIF's are operated fully unshielded no significant degradation of the performance has been observed.