RADIO-FREQUENCY SQUIDS OPERATING AT 77 K WITH A GHZ LUMPED-ELEMENT TANK-CIRCUITS

We have developed a matching scheme for the operation of a rf supercon ducting quantum interference device (SQUID) with a lumped-element tank circuit at pumping frequencies up to 1 GHz. This conventional LC reso nant circuit is inductively coupled to a matching coil, which is conne cted to the 50 Omega transmission line. We characterized the flux nois e of high-temperature rf SQUIDs at resonant frequencies between 221 an d 950 MHz. At about 900 MHz, we obtained the white flux noise of about 14.6 mu phi(0)/root Hz with a SQUID inductance L-S = 150 pH and 20 mu phi(0)/root Hz with L-S = 260 pH. Several of such tank circuits can b e driven in parallel or in series with only one cable. (C) 1998 Americ an Institute of Physics.