Quantum optics theory of electronic noise in coherent conductors

TL;DR

This paper develops a quantum optics framework for analyzing the electromagnetic noise generated by coherent conductors, linking electron transport to measurable quantum field properties and demonstrating tunable squeezing effects.

Contribution

It introduces an input-output relation for quantum currents in conductors and shows how ac-bias enables generation of squeezing, explaining recent experimental observations.

Findings

Derived an input-output relation for quantum conductors.

Showed conductors can generate tunable squeezing via ac-bias.

Explained experimental observations of squeezing in tunnel junctions.

Abstract

We consider the electromagnetic field generated by a coherent conductor in which electron transport is described quantum mechanically. We obtain an input-output relation linking the quantum current in the conductor to the measured electromagnetic field. This allows us to compute the outcome of measurements on the field in terms of the statistical properties of the current. We moreover show how under ac-bias the conductor acts as a tunable medium for the field, allowing for the generation of single- and two-mode squeezing through fermionic reservoir engineering. These results explain the recently observed squeezing using normal tunnel junctions [G. Gasse et al., Phys. Rev. Lett. 111 136601 (2013); J.-C. Forgues et al., Phys. Rev. Lett. 114 130403 (2015)].