Supercurrent and Andreev bound state dynamics in superconducting quantum point contacts under microwave irradiation

TL;DR

This paper provides a comprehensive theoretical analysis of supercurrent and Andreev bound state dynamics in superconducting quantum point contacts under microwave irradiation, revealing how microwaves influence supercurrent behavior across different regimes.

Contribution

It combines a two-level model and a microscopic Keldysh-Green function approach to analyze microwave effects on supercurrent in superconducting point contacts, offering new insights and quantitative predictions.

Findings

Microwaves induce transitions between Andreev states, suppressing supercurrent at certain phases.

Strong microwave fields distort the current-phase relation, deviating from Bessel-function behavior.

Microwave fields can enhance the critical current by connecting continuum states and Andreev states.

Abstract

We present here an extensive theoretical analysis of the supercurrent of a superconducting point contact of arbitrary transparency in the presence of a microwave field. Our study is mainly based on two different approaches: a two-level model that describes the dynamics of the Andreev bound states in these systems and a fully microscopic method based on the Keldysh-Green function technique. This combination provides both a deep insight into the physics of irradiated Josephson junctions and quantitative predictions for arbitrary range of parameters. The main predictions of our analysis are: (i) for weak fields and low temperatures, the microwaves can induce transitions between the Andreev states leading to a large suppression of the supercurrent at certain values of the phase, (ii) at strong fields, the current-phase relation is strongly distorted and the corresponding critical current does not follow a simple Bessel-function-like behavior, and (iii) at finite temperature, the microwave field can enhance the critical current by means of transitions connecting the continuum of states outside the gap region and the Andreev states inside the gap. Our study is of relevance for a large variety of superconducting weak links as well as for the proposals of using the Andreev bound states of a point contact for quantum computing applications.