100 GHZ SIS MIXER WITH IMPROVED RF MATCHING

We have designed and tested a novel superconductor-insulator-superconductor (SIS) mixer coupling scheme with an integrated millimeter-wave transformer. The impedance transformation allows larger junction sizes and easier fabrication than is possible with single junction or array mixers. Experiments with the front-end transformer mixers demonstrated mixer gains up to 10 dB and instantaneous bandwidths of 700 MHz at W-band. In addition to heterodyne mixing, we performed direct detection measurements to measure instantaneous signal bandwidth. Current responsivities of 1000 A/W were measured with a 3 dB bandwidth of 8 GHz. The direct detection performance falls at the quantum limit of one-electron-per-photon to within experimental uncertainty.