Cross-correlated dynamic resistance of a direct current superconducting quantum interference device

This paper presents experimental data on a comparative study of a dc SQUID with voltage and current bias. We introduce a cross-correlated dynamic resi stance of the device defined as a ratio R-dCV = eta(VC)/eta(IV). where eta( VC) = (delta V/delta Phi)|(A) is the slope of the voltage-to-flux character istics measured in the current bias mode ann eta(IV) = (delta I/delta Phi)| (A) is the slope of the current-to-flux characteristics measured with volta ge bias, It has been found that R-dCV may deviate strongly from the dynamic resistance observed in thr current bias mode of operation. The intrinsic e nergy resolution of the SQUID epsilon remains unchanged for both modes of o peration, but the current noise of the voltage biased device scales with th e cross-correlated dynamic resistance. In our SQUID, with the loop inductan ce L = 105 pH, epsilon is equal to 37 h in the white noise region at a temp erature of 4.2 K.