Jul 22 – 26, 2019
Europe/Rome timezone

Observation of Frequency Up-conversion Gain in SIS Junctions at Millimeter Wavelengths

Jul 25, 2019, 5:45 PM
1h 15m
Piazza Città di Lombardia (Milano)

Piazza Città di Lombardia


Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Detector readout, signal processing, and related technologies Poster session


Mr Yuto Kozuki (The University of Elector-communications)


We report on the observation of frequency up-conversion gain in superconductor-insulator-superconductor (SIS) tunnel junctions at millimeter wavelengths. So far, SIS tunnel junctions have been used as frequency down-converters with the ultra-low noise performance approaching the quantum limit and have exhibited positive gain in the down-conversion process. In principle, it is also possible to operate SIS tunnel junctions as frequency up-converters with ultra-low noise and positive gain. Our proposal is to use SIS junctions as a frequency up-converter in a novel microwave amplifier in combination with an SIS down-converter. Given that both SIS mixers (up- and down-converters) pumped by an local oscillator signal have positive conversion gains and were connected in cascade, input and output frequencies are identical with a signal gain, which has been demonstrated by our proof-of-concept test module [AIP Advances, vol. 8, no. 2, Art. no. 025206 (2018)]. For detailed analysis to improve the performance, it is important to investigate characteristics of the SIS up-converter itself. So, we have developed a test setup to measure frequency up-conversion gain in SIS tunnel junctions at millimeter wavelengths. A conventional SIS mixer with Nb/AlOx/Nb tunnel junctions was used as a frequency up-converter, which has a 20-dB input attenuator and a stainless steel WR-10 output waveguide in a 4-K cryostat. An up-converted signal from the cryostat is measured by a room temperature down-converter system with the double sideband (DSB) noise temperature of about 800 K calibrated for hot and cold loads. We observed distinct intermediate frequency responses to signal inputs from a microwave noise source (with a typical excess noise ratio of 21 dB) biased on and off, which indicated that DSB up-conversion gain in SIS junctions to be positive. Results with a continuous wave source will also be reported.

Student (Ph.D., M.Sc. or B.Sc.) Y
Less than 5 years of experience since completion of Ph.D Y

Primary authors

Mr Yuto Kozuki (The University of Elector-communications) Prof. Takafumi Kojima (National Astronomical Observatory of Japan) Prof. Wenlei Shan (National Astronomical Observatory of Japan) Prof. Yoshinori Uzawa (National Astronomical Observatory of Japan)

Presentation materials