Magnetically induced Josephson nano-diodes in field-resilient superconducting microwave circuits

TL;DR

This paper demonstrates that niobium-based superconducting circuits with nano-constrictions exhibit a magnetic-field-induced Josephson-diode effect, enhancing their performance for high-field quantum applications.

Contribution

It introduces a novel field-induced Josephson-diode effect in niobium nano-constriction circuits and models its impact on circuit nonlinearity and performance.

Findings

Field-induced asymmetry in bias-flux response observed.

Diode effect enhances circuit figures of merit in magnetic fields.

Bimodal Kerr nonlinearity demonstrated in the diode state.

Abstract

The development of nonlinear and frequency-tunable superconducting microwave circuits for operation in large magnetic fields is of high relevance for hybrid quantum systems such as spin resonance spectrometers, microwave quantum magnonics, dark matter axion detectors or flux-mediated optomechanics. With these exciting perspectives in mind, we investigate niobium-based circuits with integrated nano-constriction quantum interferometers in magnetic in-plane fields of up to several hundred mT. Our experiments reveal an unexpected and pronounced field-induced asymmetry in the bias-flux response of the circuits, which is demonstrated to originate from a field-induced Josephson-diode effect within the nano-constrictions and which enhances the circuit figures of merit in a magnetic field. An intuitive macroscopic Josephson-diode model attributes the effect to inhomogeneous constriction properties and provides us with the diode current-phase relation as a function of the in-plane field. Finally, we demonstrate that in the diode-state the circuit Kerr nonlinearity is bimodal in frequency, not only eliminating alternative explanations for the bias-flux-asymmetries but also being potentially useful for quantum circuit applications. Overall, our report underlines the potential of niobium nano-constriction circuits for high-field hybrid quantum systems, provides a conceptually simple explanation for the diode effect in superconducting nano-structures, and reveals the untapped potential of combining Josephson nano-diodes with microwave quantum circuits.