Noise analysis of the double-loop SQUID with unshunted junctions

The unshunted (un) SQUID isa two-junction device whose Josephson junctions are damped at high frequencies only. Single-valued rather than hysteretic b ehaviour on the negative resistance region is obtained by using a voltage b ias rather than a current bias. We have studied numerically the noise prope rties of the un SQUID with a double-loop (dl) washer configuration, in whic h the SQUID inductance is capacively split into two loops. Our simulations with beta(c) = 0.7 and beta(l) = 0.5 - 3 suggest that noise level in the un dl SQUID depends more weakly on the device parameters than in the un SQUID . The best energy resolution obtained in the smooth area of the IV curves i s epsilon approximate to 5k(B)T root LC but in narrow pockets in the non-sm ooth region epsilon approximate to 3k(B)T root LC is approached.