Superconducting single-mode contact as a microwave-activated quantum interferometer

TL;DR

This paper demonstrates how a superconducting quantum point contact acts as a microwave-activated interferometer, with interference effects significantly enhancing subgap current and enabling potential applications in spectroscopy and detection.

Contribution

It reveals the impact of microwave fields on Andreev levels in superconducting contacts, introducing a new interferometric mechanism for controlling subgap current.

Findings

Microwave fields induce Landau-Zener transitions in Andreev levels.

Interference causes oscillations in current as a function of inverse bias voltage.

Subgap current can increase by several orders of magnitude.

Abstract

The dynamics of a superconducting quantum point contact biased at subgap voltages is shown to be strongly affected by a microwave electromagnetic field. Interference among a sequence of temporally localized, microwave-induced Landau-Zener transitions between current carrying Andreev levels results in energy absorption and in an increase of the subgap current by several orders of magnitude. The contact is an interferometer in the sense that the current is an oscillatory function of the inverse bias voltage. Possible applications to Andreev-level spectroscopy and microwave detection are discussed.