Experimental test of the high-frequency quantum shot noise theory in a quantum point contact

We report on direct measurements of the electronic shot noise of a quantum point contact at frequencies nu in the range 4-8 GHz. 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 quantum point contact drain-source voltage V-ds are comparable to the photon energy h nu leading to observation of the shot noise suppression when V-ds < h nu/e. Our measurements provide the first complete test of the finite frequency shot noise scattering theory without adjustable parameters.