Influence of the signal coil on DC-SQUID dynamics

The dynamics of the dc-SQUID in the presence of a signal coil was studied. The signal coil creates an additive parasitic capacitance between the junctions and its self-resonance imports new features to the SQUID dynamics. Our results suggest that if a SQUID with smooth characteristics and low noise properties is desired, all the resonances present in the SQUID ring or in the flux coupling circuit should be damped properly. Low attenuation yields a system with high gain but with higher excess noise. On the other hand, heavy damping of the device yields low gain and a high noise level and thus a compromise is necessary.