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Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI

An SIS-mixer-based amplifier for multi-pixel heterodyne receivers

Yoshinori Uzawa, Takafumi Kojima, Yuto Kozuki, Yasunori Fuji, Akihira Miyachi, Tomonori Tamura, Shohei Ezaki, Wenlei Shan

Published Dec 12, 2020• 8 citations
Publisher

Abstract

We are investigating a possible microwave amplifier with low noise and low power consumption at cryogenic temperature for large scale multi-pixel heterodyne superconductor-insulator-superconductor (SIS) receivers at millimeter and submillimeter wavelengths. We propose the use of SIS junctions as amplifier elements based on quasi-particle mixing. By connecting an SIS up-converter and an SIS down-converter in series with gain in both converters, a lownoise and low-power-consumption high-frequency amplifier can be obtained in principle. A proof-of-concept study has been made by configuring an amplifier with two Nb/Al-AlOx/Nb mixers in the 150-GHz band in a standard noise and gain measurement setup at 4 K with a microwave noise source as an input signal. We observed a maximum gain of more than 10 dB and a minimum noise temperature of less than 10 K, which suggests that our proposed SIS amplifier is capable for multi-pixel SIS receivers. On the other hand, we also observed a periodical behavior in frequency dependence of the measured noise temperature and gain due to a standing-wave effect between the two SIS mixers, which is a problem to be solved.

DOI
10.1117/12.2563183

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We are investigating a possible microwave amplifier with low noise and low power consumption at cryogenic temperature for large scale multi-pixel heterodyne superconductor-insulator-superconductor (SIS) receivers at millimeter and submillimeter wavelengths. We propose the use of SIS junctions as amplifier elements based on quasi-particle mixing. By connecting an SIS up-converter and an SIS down-converter in series with gain in both converters, a lownoise and low-power-consumption high-frequency amplifier can be obtained in principle. A proof-of-concept study has been made by configuring an amplifier with two Nb/Al-AlOx/Nb mixers in the 150-GHz band in a standard noise and gain measurement setup at 4 K with a microwave noise source as an input signal. We observed a maximum gain of more than 10 dB and a minimum noise temperature of less than 10 K, which suggests that our proposed SIS amplifier is capable for multi-pixel SIS receivers. On the other hand, we also observed a periodical behavior in frequency dependence of the measured noise temperature and gain due to a standing-wave effect between the two SIS mixers, which is a problem to be solved.
We propose a low-noise and low-power-consumption microwave amplifier using superconductor-insulator-superconductor (SIS) mixers as quasi-particle frequency up- and down-converters pumped by a Josephson array oscillator in the millimeter-wave band. A proof-of-concept study of an amplifier with two W-band waveguide mixers using Nb/Al-AlOx/Nb junctions in a cascade connection demonstrated an average gain of 6 dB and a noise temperature of 12 K from nearly DC to 5 GHz. We also designed and fabricated a Josephson array oscillator at 100 GHz, which consisted of 31 overdamped Josephson junctions placed at each half-wavelength in an Nb microstrip line. The estimated output power of the oscillator was 0.2 μW at 100 GHz, which can be increased by increasing the number of the oscillator junctions. These results suggest that the proposed SIS mixer-based amplifier is suitable for on-chip integrated circuits to be implemented in large-scale multipixel SIS receivers and quantum computers.
This paper introduces a potential low-power-consumption and low-noise microwave amplifier operated at cryogenic temperature, essential for large-scale multi-pixel heterodyne receivers and fault-tolerant quantum computers. The amplifier employs two millimeter-wave superconductor-insulator-superconductor (SIS) mixers as amplifying elements and a millimeter-wave Josephson array oscillator as the local oscillator source. A proof-of-concept experiment utilizing waveguide SIS mixer modules demonstrated an average gain of approximately 7.5 dB and a noise temperature of around 10 K at microwave frequencies. Additionally, a waveguide Josephson array oscillator module, developed to validate the design, exhibited an output power of roughly 52 nW, estimated from the response of a waveguide SIS detector connected to the oscillator module. These findings indicate the feasibility of realizing a monolithically integrated amplifier chip incorporating SIS mixers and a Josephson array oscillator.
This paper describes a low-noise microwave amplifier based on up- and down-frequency-conversion processes in quasiparticle superconductor–insulator–superconductor (SIS) tunnel junctions. The SIS amplifier was configured with two SIS frequency-converter modules and a cryogenic millimeter-wave isolator inserted between them. Moreover, a local oscillator (LO) using millimeter-wave attenuators and a phase shifter was considered. This setup allowed the control of individual LO power and differential phase in these SIS frequency converters to optimize the amplifier performance. The SIS amplifier showed noise temperatures as low as 11 K and a 6–8 dB gain from nearly DC to 5 GHz. The attained microwave performance is promising for obtaining large-format arrays, such as multibeam heterodyne receivers. Moreover, this two-frequency-converter concept based on SIS junctions might enable microwave applications, such as wideband non-reciprocal circuits in isolators, gyrators, and circulators, which are essential devices in the quantum computing and radio astronomy fields.
We propose an optimization method for a superconductor-insulator-superconductor (SIS) mixer-based amplifier circuit that employs SIS up- and down-converters. Such a novel amplifier configuration could enable superior low-noise performance for future broadband amplifier systems, such as those for large arrays of superconducting sensors or qubits. Optimization was achieved by identifying a solution in which the mutually dependent impedances of the SIS mixers converge under given conditions. A circuit design using this method predicted an amplifier gain of approximately 20 dB and a noise temperature of approximately 2 K at 4 K operation when practical current-voltage characteristics of Nb SIS junctions are used in the simulation. To verify the validity of this method, an amplifier circuit was prepared using waveguide Nb/AlOx/Nb mixer modules. By varying the phase delay between the two SIS mixers, changes in gain were observed, resulting from different convergence conditions of their mutually dependent impedances, which closely matched the predictions made using this method. These results are promising for the development of an integrated circuit including SIS amplifiers and superconducting detector arrays, with bandwidths of 10 GHz or above. This may also enable novel nonreciprocal microwave circuits such as gyrators, isolators, and circulators.
The authors have made a detailed study of the gain and noise of a SIS (superconductor-insulator-superconductor) heterodyne receiver at 345 GHz. An array of two Nb-Al/sub 2/O/sub 3/-Nb SIS junctions in series are used as the mixing element. The array is operated in a waveguide mount with a backshort and an E-plane tuner. The best receiver noise temperature achieved is 140 K DSB (double sideband). The embedding impedances were determined by fitting theory to the measured pumped curves. High-quality fits were obtained, providing the first detailed test of the Tucker-theory at frequencies above 300 GHz. The impedances found by this method are in very good agreement with impedances measured in a scale model at 3.3 GHz. From these embedding impedances, the gain and noise of the mixer were calculated over a full bias range using the Tucker theory in the three-port low-IF approximation. The measured dependence of mixer gain and noise on bias voltage, pump power and embedding impedance is in good agreement with theory. However the absolute values show discrepancies that appear to be independent of the bias parameters of the mixer.>
The possibility of overcoming the main drawbacks of the traditional series arrays by parallel connection of the SIS (superconductor-insulator-superconductor) junctions for DC and IF are demonstrated experimentally. The proposed mixing elements avoid the influence of the junction nonuniformity in the array, provide the optimal matching on both RF input and IF output, and tune out junction capacitance. Experimentally tested arrays contained up to eight high-quality Nb-AlO/sub x/-Nb junctions with R/sub n/=20-70 Omega at junction area 8/14 mu m/sup 2/. The best values of T/sub r/ (SSB) were measured to as low as 5 K on the mixer cold input flange in the 45-55-GHz bandwidth at an ambient temperature of 4.2 K. A mixer gain of up to 10 dB was obtained. The gain values were limited by bias stability at very high or even negative array output impedance. An experimental receiver noise temperature (SSB) of less than 20 K has been achieved.