Direct current superconducting quantum interferometers with asymmetric shunt resistors

Abstract

We have investigated asymmetrically shunted Nb/Al-AlO${}_x$/Nb direct current (dc) superconducting quantum interference devices (SQUIDs). While keeping the total resistance $R$ identical to a comparable symmetric SQUID with $R^{-1}=R_1^{-1}+R_2^{-1}$, we shunted only one of the two Josephson junctions with $R=R_{1,2}/2$. Simulations predict that the optimum energy resolution $\epsilon$ 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 $\epsilon \approx 32\hslash$ for an asymmetric SQUID with an inductance of $22\mathrm{pH}$. For a comparable symmetric device $\epsilon =110\hslash$ was achieved, confirming our simulation results.

5 pages, 4 figures

References in corpus (3)

• Voltage-flux-characteristics of asymmetric dc SQUIDs
• A Numerical Treatment of the Rf SQUID: II. Noise Temperature
• A Numerical Treatment of the Rf SQUID: I. General Properties and Noise Energy

Cited by in corpus (3)

• Self-field effects in window-type Josephson tunnel junctions
• Sub-μm Josephson Junctions for Superconducting Quantum Devices
• Flux Dependent Crossover Between Quantum and Classical Behavior in a dc-SQUID