Mm-wave harmonic generation in an array of SIS junctions

We report the first experimental off-chip detection of frequency multiplication in a distributed array of Superconductor-Insulator-Superconductor (SIS) junctions. A test device consisting of series array of 68 Nb/Al-AlOx/Nb tunnel junctions was designed to study generation of the second harmonic. We measured extremely sharp spectral signals, associated with the 7 2 frequency multiplication. Distinct single and multi-photon processes were observed in the test device response operated in quantum mode. The mechanism of device saturation was experimentally studied. The test device when connected to the input of an SIS mixer, and pumped, showed 10-20% increase in the SIS junction dark current