Phase-dependent microwave response of a graphene Josephson junction

TL;DR

This study investigates the phase-dependent microwave response of a graphene-based Josephson junction embedded in a superconducting circuit, revealing insights into supercurrent dynamics and non-equilibrium populations relevant for quantum circuit engineering.

Contribution

It provides a comprehensive circuit model and experimental analysis of a graphene Josephson junction's admittance, linking microscopic transport mechanisms to microwave response.

Findings

Extracted phase-dependent junction admittance corrected for SQUID self-screening

Decomposed admittance into current-phase relation and phase-dependent loss

Deduced a non-equilibrium population lifetime of ~17 ps

Abstract

Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in-situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing an rf SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we deduce a lifetime of ~17 ps for non-equilibrium populations.