Electron-photon interaction in a quantum point contact coupled to a microwave resonator

TL;DR

This paper investigates how a microwave resonator coupled to a quantum point contact exhibits modified photon states and noise properties, revealing two-photon processes and backaction effects through theoretical analysis.

Contribution

It extends $P(E)$ theory to steady state and analyzes cavity-electron interactions, providing new insights into quantum noise and photon statistics in mesoscopic conductors.

Findings

Cavity reaches a thermal state at lowest order with emission noise.

Two-photon processes dominate at higher coupling, reducing photon bunching.

Modified noise properties of the conductor are quantitatively predicted.

Abstract

We study a single-mode cavity weakly coupled to a voltage-biased quantum point contact. In a perturbative analysis, the lowest order predicts a thermal state for the cavity photons, driven by the emission noise of the conductor. The cavity is thus emptied as all transmission probabilities of the quantum point contact approach one or zero. Two-photon processes are identified at higher coupling, and pair absorption dominates over pair emission for all bias voltages. As a result, the number of cavity photons, the cavity damping rate and the second order coherence $g^{(2)}$ are all reduced and exhibit less bunching than the thermal state. These results are obtained with a Keldysh path integral formulation and reproduced with rate equations. They can be seen as a backaction of the cavity measuring the electronic noise. Extending the standard $P(E)$ theory to a steady-state situation, we compute the modified noise properties of the conductor and find quantitative agreement with the perturbative calculation.