SIS mixers

Small area superconducting thin film tunnel junctions have properties which make them suitable for high frequency (∝ 100 GH) heterodyne receivers. Both pair and single quasiparticle tunneling is present in the devices, but pair tunneling is found to be excessively noisy, whereas quasiparticle tunneling apparently gives HOPE of near quantum noise limited performance. The physical effect involved is photon assisted quasiparticle tunneling first observed by Dayem and Martin. A recent theory by Tucker has allowed a good understanding of many aspects of the phenomenon so that considerable HOPE exists for successful application of SIS mixer devices in fields such as millimeter and submillimeterwave astronomy. Some of the laboratory experiments and receiver construction efforts are reviewed in this article.