FREQUENCY READOUT OF RELAXATION OSCILLATION SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES IN THE GHZ REGIME

The output of relaxation oscillation superconducting quantum interfere nce devices (ROSs) consists of a sequence of voltage pulses with a fre quency that depends on the flux that is applied to the ROS. In this pa per, a theoretical model for the flux-to-frequency conversion of a ROS is presented, and this model is validated in practice for oscillation frequencies up to 7 GHz. The experiments have been performed on more than ten different ROSs and the model was able to fit all measured dat a, which illustrates the versatility of the model. Furthermore, a simp le flux locked loop based on frequency readout of a ROS in the GHz reg ime is presented. The measured flux noise, root S-Phi = 2.5 mu Phi(0)/ root Hz, corresponding to an energy resolution epsilon approximate to 600h, is probably not intrinsic to the ROSs, but due to the readout el ectronics. (C) 1996 American Institute of Physics.