Quantum limited heterodyne detection in superconducting non-linear transmission lines at sub-millimeter wavelengths

Abstract

A non-linear superconducting transmission line has been successfully employed in heterodyne detection of sub-millimeter waves. In our experiments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15×40 μm, with a critical current density of about 2500 A/cm2 is used as a distributed mixer element. We have demonstrated that quantum limited sensitivity can be achieved with this type of device. At 460 GHz, a Y-factor of 2.5 has been recorded, corresponding to a double-side-band receiver noise temperature of 80 K. The double-side-band conversion loss is about 1 dB and the mixer noise temperature is estimated to be 18(±10) K.