Non-Classical Radiation Emission By A Coherent Conductor

TL;DR

This paper provides experimental evidence that microwave radiation emitted by a normal conductor at ultra-low temperatures can exhibit non-classical properties such as squeezing and entanglement, challenging classical assumptions.

Contribution

It demonstrates for the first time that a normal conductor's microwave emission can be non-classical, showing squeezing and entanglement in the emitted radiation.

Findings

Quadrature variance below vacuum level indicating squeezing.

Detection of entanglement between two frequency modes.

Evidence of non-classical radiation from a normal conductor.

Abstract

We report experimental evidence that the microwave electromagnetic field generated by a normal conductor, here a tunnel junction placed at ultra-low temperature, can be non-classical. By measuring the quadratures of the electromagnetic field at one or two frequencies in the GHz range, we demonstrate the existence of squeezing as well as entanglement in such radiation. In one experiment, we observe that the variance of one quadrature of the photo-assisted noise generated by the junction goes below its vacuum level. In the second experiment, we demonstrate the existence of correlations between the quadratures taken at two frequencies, which can be stronger than allowed by classical mechanics, proving that the radiation at those two frequencies are entangled.