Enhanced superconducting diode effect in a gate-tunable double-loop SQUID

The superconducting diode effect is a non-reciprocal transport phenomenon which can arise in superconducting quantum interference devices (SQUIDs) due to interference between different supercurrent harmonics. We report measurements on a double-loop SQUID with two gate-tunable Josephson junctions in each interference branch, leading to a current-phase relationship (CPR) tunable harmonic content. We demonstrate an ability to operate this double-loop SQUID as a gate and flux-tunable superconducting diode, and we observe a maximum diode efficiency exceeding 50%, a significant improvement over previous realizations of SQUID diodes. The observed effects are well explained by a model of the flux-dependent switching current oscillations calculated using the expected CPR of the full double-loop SQUID in multiple gate voltage configurations, suggesting precise control over the CPR of this device, and paving the way for more complex superconducting devices with tailored CPRs and EPRs.