Quantum Phase Diffusion in a Small Underdamped Josephson Junction

TL;DR

This paper demonstrates quantum phase diffusion in a small underdamped Josephson junction across a wide temperature range, highlighting the transition from thermal activation to macroscopic quantum tunneling as the dominant escape mechanism.

Contribution

It introduces a two-step transition model for the switching process and experimentally verifies the transition rate behavior in different regimes.

Findings

Transition rate follows Arrhenius law in thermal regime

Enhanced transition rate in the quantum tunneling regime

Observation of quantum phase diffusion over 25-140 mK

Abstract

Quantum phase diffusion in a small underdamped Nb/AlO$_x$/Nb junction ($\sim$ 0.4 $\mu$m$^2$) is demonstrated in a wide temperature range of 25-140 mK where macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We propose a two-step transition model to describe the switching process in which the escape rate out of the potential well and the transition rate from phase diffusion to the running state are considered. The transition rate extracted from the experimental switching current distribution follows the predicted Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes dominant.