QUANTUM LIMITED HETERODYNE-DETECTION IN SUPERCONDUCTING NONLINEAR TRANSMISSION-LINES AT SUBMILLIMETER WAVELENGTHS

A non-linear superconducting transmission line has been successfully e mployed in heterodyne detection of sub-millimeter waves. In our experi ments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15 x 40 mu m, with a critical current density of about 2500 A/cm(2) is used as a distrib uted mixer element. We have demonstrated that quantum limited sensitiv ity can be achieved with this type of device. At 460 GHz, a Y-factor o f 2.5 has been recorded, corresponding to a double-side-band receiver noise temperature of 80 K, The double-side-band conversion loss is abo ut 1 dB and the mixer noise temperature is estimated to be 18(+/- 10) K. (C) 1995 American Institute of Physics.