High frequency shot noise of phase coherent conductors

We report on direct measurements of the electronic shot noise of a Quantum Point Contact (QPC) at frequencies v in the range 4-8GHz. The very small energy scale used ensures energy independent transmissions of the few transmitted electronic modes and their accurate knowledge. Both the thermal energy and the QPC drain-source voltage V-ds are comparable to the photon energy leading to the observation of the shot noise suppression when V-ds < hv/e. The measurements provide the first direct comparison to the high frequency shot noise scattering theory without adjustable parameters. Furthermore, the developed method allows cross-correlation measurements and computation of higher moments of current noise. This possibility is demonstrated by the measurements of the fluctuations of the power emitted by a biased tunnel junction.