Washing out of the 0-pi transition in Josephson junctions

TL;DR

This paper investigates how quasi-particles and electromagnetic environments influence the 0-pi transition in Josephson junctions, revealing that photon-assisted quasi-particle absorption can dynamically switch states and obscure the transition.

Contribution

It introduces a Born-Markov framework to analyze the impact of quasi-particles and electromagnetic coupling on the 0-pi transition in Josephson junctions, highlighting the dynamic switching mechanism.

Findings

Quasi-particles can significantly alter the 0-pi transition.

Photon-assisted absorption enables dynamic switching between 0 and pi states.

The 0-pi transition can be washed out by environmental effects.

Abstract

We consider a Josephson junction formed by a quantum dot connected to two bulk superconductors in presence of Coulomb interaction and coupling to both an electromagnetic environment and a finite density of electronic quasi-particles. In the limit of large superconducting gap we obtain a Born-Markov description of the system dynamics. We calculate the current-phase relation and we find that the experimentally unavoidable presence of quasi-particles can dramatically modify the 0-pi standard transition picture. We show that photon-assisted quasi-particles absorption allows the dynamic switching from the 0- to the pi-state and vice-versa, washing out the 0-pi transition predicted by purely thermodynamic arguments.