Distributed quasiparticle mixing in a non-linear transmission line at sub-millimeter wavelengths

A new class of distributed mixer based on the non-linear quasiparticle tunnel current in a superconductor-insulator-superconductor transmission line has been proposed and tested. The Nb/Al/AlOx/Nb junctions used in our mixers are typically 200 nm wide and are between 1 and 2 guided wavelengths long. Compared with the traditional sub-millimeter lumped element quasiparticle mixer, the distributed mixer requires lower critical current densities, lower magnetic field as well as simpler tuning circuitry. Experiments have been performed in various sub-millimeter frequency bands. Receiver noise temperatures of 66 K at 460 GHz, 210 K at 630 GHz and 600 K at 780 GHz have been measured. These noise temperatures are comparable to or slightly better than the noise temperatures of the corresponding lumped element mixers.