Conversion efficiency of a large-β DC-SQUID with a resistively shunted inductance

The conversion efficiency between a signal magnetic flux and the output power of a large-β dc SQUID, i.e., a SQUID with a modulation parameter β larger than unity, have been studied theoretically. In our investigation the inductance of the SQUID was shunted by using a damping resistor. The dependence of the output power on such SQUID parameters as β, the McCumberparameter β_cand the damping parameter γ=R_sR_d(R_sand R_dare the shunt and the damping resistances, respectively) was investigatedin detail. It has been shown that an order-of-magnitude increase in the output power can be realized with a large-β SQUID without a degradation of noise characteristics, compared with thecaseof β=1. It has also been shown that the values of β_c=0.4 and γ=1areoptimum with regard to a large output power and a low-noise operation of the SQUID.