Theory of microwave-assisted supercurrent in quantum point contacts

TL;DR

This paper develops a microscopic theory describing how microwave fields influence supercurrent in quantum point contacts, revealing suppression, reversal, and enhancement effects depending on field strength and temperature.

Contribution

It introduces a comprehensive microscopic model for microwave effects on supercurrent in quantum point contacts of arbitrary transmission.

Findings

Supercurrent suppression at certain phases under low temperatures and weak fields.

Reversal of current direction at strong microwave fields.

Enhancement of critical current at finite temperatures.

Abstract

We present a microscopic theory of the effect of a microwave field on the supercurrent through a quantum point contact of arbitrary transmission. Our theory predicts that: (i) for low temperatures and weak fields, the supercurrent is suppressed at certain values of the superconducting phase, (ii) at strong fields, the current-phase relation is strongly modified and the current can even reverse its sign, and (iii) at finite temperatures, the microwave field can enhance the critical current of the junction. Apart from their fundamental interest, our findings are also important for the description of experiments that aim at the manipulation of the quantum state of atomic point contacts.