Measurements of Phase Dynamics in Planar Josephson Junctions and SQUIDs

TL;DR

This paper experimentally studies the phase dynamics of planar Josephson junctions and SQUIDs in InAs/Al heterostructures, revealing a gate-tunable crossover from quantum tunneling to phase diffusion and demonstrating phase locking effects.

Contribution

It provides the first detailed experimental analysis of phase dynamics in epitaxial InAs/Al Josephson devices, including gate and flux tuning of the transition temperature.

Findings

Observation of temperature-dependent crossover from quantum tunneling to phase diffusion.

Switching probability distributions consistent with small shunt capacitance and moderate damping.

Phase locking causes differences in switching currents between isolated JJs and SQUID configurations.

Abstract

We experimentally investigate the stochastic phase dynamics of planar Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) defined in epitaxial InAs/Al heterostructures, and characterized by a large ratio of Josephson energy to charging energy. We observe a crossover from a regime of macroscopic quantum tunneling to one of phase diffusion as a function of temperature, where the transition temperature $T^{*}$ is gate-tunable. The switching probability distributions are shown to be consistent with a small shunt capacitance and moderate damping, resulting in a switching current which is a small fraction of the critical current. Phase locking between two JJs leads to a difference in switching current between that of a JJ measured in isolation and that of the same JJ measured in an asymmetric SQUID loop. In the case of the loop, $T^*$ is also tuned by a magnetic flux.