Electron–photon correlations and the third moment of quantum noise

Abstract

The radiation generated by a quantum conductor should be correlated with the electrons crossing it. We have measured the correlation between the fluctuations of the high-frequency electromagnetic power generated by a tunnel junction at very low temperature and the low-frequency voltage fluctuations across it. This quantity corresponds to a third-order correlator of the electromagnetic field. At low-voltage bias, i.e. when the junction emits no radiation into the impedance-matched vacuum connected to it, we observe that the voltage fluctuations of the electric signal generated by the junction has zero third moment. Yet we show by a careful analysis of environmental contributions that the intrinsic third moment of the high-frequency current fluctuations in the junction is given by e ^2 I .