Low-noise 1 THz superconductor-insulator-superconductor mixer incorporating a NbTiN/SiO2/Al tuning circuit

Low-noise heterodyne mixing at 1 THz is demonstrated in a quasioptical mixe r incorporating Nb superconductor-insulator-superconductor tunnel junctions and a NbTiN/SiO2/Al tuning circuit. Receiver noise temperatures as low as 250 K at 850 GHz, 315 K at 980 GHz, and 405 K at 1015 GHz are measured-a fa ctor of 2 improvement in sensitivity versus state-of-the-art 1 THz receiver s, which incorporate normal metal tuning circuits. An analysis of the recei ver sensitivity at 980 GHz demonstrates that NbTiN is low loss up to simila r to1 THz. (C) 2001 American Institute of Physics.