We have investigated asymmetrically shunted Nb/Al-AlOx/Nb direct current
(dc) superconducting quantum interference devices (SQUIDs). While keeping the
total resistance R identical to a comparable symmetric SQUID with R−1=R1−1+R2−1, we shunted only one of the two Josephson junctions with
R=R1,2/2. Simulations predict that the optimum energy resolution
ϵ and thus also the noise performance of such an asymmetric SQUID can
be 3--4 times better than that of its symmetric counterpart. Experiments at a
temperature of 4.2\,K yielded ϵ≈32ℏ for an asymmetric
SQUID with an inductance of 22pH. For a comparable symmetric device
ϵ=110ℏ was achieved, confirming our simulation results.Comment: 5 pages, 4 figure