Josephson radiation and shot noise of a semiconductor nanowire junction

We measured the Josephson radiation emitted by an InSb semiconductor nanowire junction utilizing photon assisted quasiparticle tunneling in an AC-coupled superconducting tunnel junction. We quantify the action of the local microwave environment by evaluating the frequency dependence of the inelastic Cooper-pair tunneling of the nanowire junction and find the zero frequency impedance \(Z(0)=492\,\Omega\) with a cutoff frequency of \(f_0=33.1\,\)GHz. We extract a circuit coupling efficiency of \(\eta\approx 0.1\) and a detector quantum efficiency approaching unity in the high frequency limit. In addition to the Josephson radiation, we identify a shot-noise contribution with a Fano factor \(F\approx1\), consistently with the presence of single electron states in the nanowire channel.