APPARATUS AND METHOD FOR ADJUSTING OPERATING POINT OF SQUID

摘要

PROBLEM TO BE SOLVED: To provide an apparatus for adjusting a bias voltage of a SQUID (superconducting quantum interference device) which can automatically and appropriately adjust a bias current in a short time. SOLUTION: A 50 kHz sine wave current with an adjustable magnetic field bias applied by a magnetic field bias source 17 is sent to a coil 12, thereby generating a magnetic field to a SQUID 10. In this state, an output voltage is extracted from the SQUID 10. An amplitude of the magnetic field of the extracted output voltage is half a cycle of a magnetic field-voltage characteristic. The voltage is filtered by a filter 14 and only a 50 kHz component is extracted. The extracted signal component is rectified by a rectifier 15 and converted to a d.c. voltage. The magnetic field bias source 17 is adjusted to obtain a maximum value while seen through a voltage monitor 16.