Photon pair shot noise in electron shot noise

TL;DR

This paper demonstrates photon pair emission from a tunnel junction, linking electron shot noise and photon shot noise through dual electromagnetic and charge transport representations, with experimental data supported by quantum optics theory.

Contribution

It provides the first measurement of photon shot noise from a tunnel junction, revealing non-classical photon pair emission and connecting electron and photon noise descriptions.

Findings

Photon pair emission observed with Fano factor above unity.

Quantum optics theory accurately models photon shot noise.

Experimental data confirms the duality between charge transport and electromagnetic field representations.

Abstract

There exists a fascinating dual representation of the electric ac current flowing through a normal conductor. On the one hand, it can be understood in terms of charge transport. On the other hand, it consists in an electomagnetic field guided by conducting structures embedded in an insulator. The former point of view, in its quantum version, is particularly adapted to describe the electron shot noise in a coherent conductor, like a tunnel junction at ultra-low temperature. However, when the junction is appropriately biased by a dc and an ac voltage, the noise it generates is best analyzed using the latter representation and the tools of quantum optics, as the radiation exhibits clear signs of non-classicality. Herein, we report the measurement of the statistics of photons emitted by such a tunnel junction. We observe a photon shot noise characteristic of photon pair emission, as its Fano factor for small signal is above unity. The theory of electron shot noise, dealing exclusively with the tunneling of charges through the junction, quantitatively fits the data from which photon shot noise is extracted. This experiment thus provides a clear link between the dual representations.