100 GHz SIS mixer with improved RF matching

A novel superconductor-insulator-superconductor (SIS) mixer coupling scheme with an integrated millimeter-wave transformer has been designed and tested. 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, direct detection measurements were made 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 to within experimental uncertainty at the quantum limit of one-electron-per-photon.