Photo-assisted Andreev reflection as a probe of quantum noise

TL;DR

This paper proposes a novel detector based on Andreev reflection to measure high-frequency quantum noise in mesoscopic circuits, analyzing different circuit configurations and providing numerical estimates.

Contribution

It introduces a new photo-assisted Andreev reflection detector design for high-frequency noise measurement in mesoscopic systems.

Findings

The detector current can be expressed as a frequency integral of excess noise.

Different detector circuits show specific responses to environmental noise.

Numerical estimates demonstrate the detector's potential effectiveness.

Abstract

Andreev reflection, which corresponds to the tunneling of two electrons from a metallic lead to a superconductor lead as a Cooper pair (or vice versa), can be exploited to measure high frequency noise. A detector is proposed, which consists of a normal lead--superconductor circuit, which is capacitively coupled to a mesoscopic circuit where noise is to be measured. We discuss two detector circuits: a single normal metal -- superconductor tunnel junction and a normal metal separated from a superconductor by a quantum dot operating in the Coulomb blockade regime. A substantial DC current flows in the detector circuit when an appropriate photon is provided or absorbed by the mesoscopic circuit, which plays the role of an environment for the junction to which it couples. Results for the current can be cast in all cases in the form of a frequency integral of the excess noise of the environment weighted by a kernel which is specific to the transport process (quasiparticle tunneling, Andreev reflection,...) which is considered. We apply these ideas to the measurement of the excess noise of a quantum point contact and we provide numerical estimates of the detector current.