Determination Hanbury-Brown Twiss correlations with electrons and photons

What is the statistics of the photons emitted by a quantum conductor? We present the first experiment addressing this question, where the electronic shot noise power of a 500$\Omega $ tunnel junction is measured in the 4-8 GHz frequency range in an Hanbury-Brown Twiss geometry (E. Zakka-Bajjani \textit{et al.} Phys. Rev. Lett. \textbf{99}, 236803 (2007)). The emitted noise is analyzed in two different manners. The fluctuations of the transmitted and reflected electronic currents are shown to be anti-correlated. The auto-correlated power fluctuations reveal that the junction emits power into the detection in the form of photons, and the emitted powers show positive cross-correlation, proportional to the squared emitted power. The photons emitted by a biased low impedance (i.e. R$_{tunnel}<