Macroscopic quantum tunneling in globally coupled series arrays of Josephson junctions

TL;DR

This paper analyzes how global coupling via an external impedance affects macroscopic quantum tunneling in Josephson junction arrays, revealing conditions that suppress or enhance tunneling rates and crossover temperatures.

Contribution

It introduces a model explaining the enhancement of MQT in large arrays through spatial-temporal charge instantons, aligning with experimental observations.

Findings

Suppression of MQT and crossover temperature in short arrays due to impedance.

Enhancement of MQT escape rate and crossover temperature in large arrays.

Explanation of experimental MQT enhancement in high-$T_c$ superconductor crystals.

Abstract

We present a quantitative analysis of an escape rate for switching from the superconducting state to a resistive one in series arrays of globally coupled Josephson junctions. A global coupling is provided by an external shunting impedance. Such an impedance can strongly suppress both the crossover temperature from the thermal fluctuation to quantum regimes, and the macroscopic quantum tunneling (MQT) in short Josephson junction series arrays. However, in large series arrays we obtain an enhancement of the crossover temperature, and a giant increase of the MQT escape rate. The effect is explained by excitation of a {\it spatial-temporal charge instanton} distributed over a whole structure. The model gives a possible explanation of recently published experimental results on an enhancement of the MQT in single crystals of high-$T_c$ superconductors.