Observation of transition from escape dynamics to underdamped phase diffusion in a Josephson junction

TL;DR

This paper investigates the transition in underdamped Josephson junctions from thermally activated switching to underdamped phase diffusion, revealing a sharp threshold behavior and proposing a comprehensive phase diagram considering dissipation and level quantization.

Contribution

It reports the first observation of the transition from thermally activated behavior to underdamped phase diffusion in Josephson junctions with small Josephson coupling.

Findings

Sharp switching threshold above crossover temperature

Proposed (T,E_J) phase diagram with multiple regimes

Dissipation and level quantization are crucial for accurate modeling

Abstract

We have investigated the dynamics of underdamped Josephson junctions. In addition to the usual crossover between macroscopic quantum tunnelling and thermally activated (TA) behaviour we observe in our samples with relatively small Josephson coupling E_J, for the first time, the transition from TA behaviour to underdamped phase diffusion. Above the crossover temperature the threshold for switching into the finite voltage state becomes extremely sharp. We propose a (T,E_J) phase-diagram with various regimes and show that for a proper description of it dissipation and level quantization in a metastable well are crucial.