What is the counting statistics of the photons emitted by a coherent quantum conductor and how does it relate to the electrons counting statitsitics ?
This question might seem artificial, unless one notices the dual representation of the current as fermionic excitations in a quantum conductor and bosonic electromagnetic modes in the external measuring circuit. This problem was addressed by Beennaker and Schomerus (PRL 86 p700 (2001) and PRL 93 p096801 (2003)), with the spectacular prediction that a QPC could emit sub-Poissonian photons. We tested Beenakker and Schomerus’ prediction on the simplest and best understood mescocopic conductor, a tunnel junction. We developped an original method to measure photon statistics based on Hanburry-Brown and Twiss correlations and fast digitization. Our data show perfect agreement with theory for a wide range of frequency, voltage and temperature with no adjustable parameters. As the power fluctuations are found to be proportionnal to the squared emission noise power, our experiment also sheds light on the status of ’zero point’ fluctuations in quantum shot noise measurements in an HBT configuration. It is also an important step toward the detection of the predicted non-classical photon noise emitted by a quantum point contact.