Josephson quantum mechanics at odd parity

TL;DR

This paper explores the unique quantum mechanics of Josephson junctions with odd parity states, revealing how quasiparticle trapping influences supercurrent behavior across different electromagnetic environments.

Contribution

It provides a theoretical analysis of odd parity states in Josephson junctions, including effects of quasiparticle poisoning and impedance-dependent supercurrent dynamics.

Findings

Odd parity states can stabilize supercurrent in Josephson junctions.

Quasiparticle poisoning lifts the supercurrent quench in low impedance environments.

Critical impedance for Schmid transition is four times higher in odd parity states.

Abstract

A Josephson junction may be in a stable odd parity state when a single quasiparticle is trapped in an Andreev bound state. Embedding such junction in an electromagnetic environment gives rise to a special quantum mechanics of superconducting phase that we investigate theoretically. Our analysis covers several representative cases, from the lifting of the supercurrent quench due to quasiparticle poisoning for a low ohmic impedance of the environment, to a Schmid transition in a current-biased junction that for odd parity occurs at four times bigger critical impedance. For intermediate impedances, the supercurrent in the odd state is higher than in the even one.