Resonant enhancement of MQT in Josephson junctions: the influence of coherent two-level systems

TL;DR

This paper presents a theoretical analysis of how coherent two-level systems within Josephson junctions can resonantly enhance macroscopic quantum tunneling, especially affecting the crossover temperature between thermal and quantum regimes under magnetic fields.

Contribution

It introduces a model showing how coherent two-level systems cause a resonant suppression of the potential barrier, leading to a peak in the crossover temperature dependence on magnetic flux.

Findings

Predicted a narrow peak in $T_{cr}(\

Enhanced understanding of the role of two-level systems in Josephson junction quantum behavior.

Quantitative explanation of the resonant suppression effect due to Rabi oscillations.

Abstract

We report a theoretical study of the macroscopic quantum tunneling (MQT) in small Josephson junctions containing randomly distributed two-level systems. We focus on the magnetic field dependent crossover temperature $T_{cr}$ between the thermal fluctuation and quantum regimes of switching from the superconducting (the zero-voltage) state to a resistive one. In the absence of two-levels systems the crossover temperature shows a smooth decrease with an applied magnetic field characterized by an external flux $\Phi$. Beyond that we predict a narrow peak in the dependence of $T_{cr}(\Phi)$ occurring in the intermediate range of $\Phi$. The effect becomes more pronounced as the junction size increases. We explain this effect quantitatively by a strong resonant suppression of a potential barrier for the Josephson phase escape that is due to the coherent quantum Rabi oscillations in two-level systems present in the junction.