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 Vds are comparable to the photon energy hnu leading to observation of the shot noise suppression when $V_{ds}<h\nu \mathrm{/}e$. Our measurements provide the first complete test of the finite frequency shot noise scattering theory without adjustable parameters.