Responsivity of SIS Tunnel Junctions to mm-Wave Radiation

Hans J. Hartfuss, M. Tutter

K. H. Gundlach, Hans J. Hartfuss, Kikuo Okuyama

The theory of photon-assisted tunneling is outlined. The I–U characteristic with and without radiation and the junction conductance are evaluated for the temperature of 4.2 K. From these results the current responsivity ηc and the voltage responsivity ηv are derived. At a frequency of 72 GHz the theory yields the maximum values ηc = 3.3 × 103 A/W and for a 100Ω junction ηv = 2.5 × 108 V/W. Leakage current and other shortcomings of the real junctions reduce these values to ηc ≈︁ 3 × 103 A/W and ηv ≈︁ 106 V/W.

D. N. Langenberg, William H. Parker, Barry N. Taylor

Bhushan Billade, Alexey Pavolotsky, Victor Y. Belitsky

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 in the 190-210 GHz band. The SIS array was exited with microwave radiation at 3-mm band using a quasi-optically coupled Gunn oscillator, and the output response of the device was studied using a double-sideband SIS mixer operating in the 163-211 GHz range with 4-8 GHz IF bandwidth. We measured extremely sharp spectral signals, associated with the ×2 frequency multiplication by the SIS array. Single- and multi-photon processes were observed in the response of SIS tunnel junction-array to the applied microwave radiation, confirming device operation in the quantum mode. The output power of the multiplied signal increases linearly with the power of the pumping signal up to certain level and them saturates. In attempt to verify that the device produces noticeable power, the output of the test device was connected to the LO port of the SIS mixer, and an increase of 10%-20% in the SIS mixer dark current was observed. Further development of the demonstrated principle of frequency multiplication may lead to a practical frequency multiplier device.

Richard K. Elsley, Albert J. Sievers

Bhushan Billade, Alexey Pavolotsky, Victor Y. Belitsky

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 × 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.