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Annual Meeting Optical Society of America

Observation of thermal noise squeezing via a Josephson parametric amplifier

B. Yurke, P. G. Kaminsky, Ronald Earle Miller, Edward A. Whittaker, A. D. Smith, Arnold H. Silver, R. W. Simon

Published Jan 1, 1987• 0 citations
Publisher

Abstract

We are engaged in a research effort to generate squeezed microwaves at K-band frequencies (18–26.5 GHz) using a Josephson parametric amplifier. As a milestone in this effort we have demonstrated 4-K thermal noise squeezing at 19 GHz. A superconductor–insulator–superconductor (SIS) mixer was employed as the detector. The parametric amplifier and SIS mixer were both cooled to 4.2 K, and care was taken using cold attenuators and isolators to make negligible the amount of room-temperature microwave noise coupled into the cryostat.

DOI
10.1364/oam.1987.tui5

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We are engaged in a research effort to generate squeezed microwaves at K-band frequencies (18–26.5 GHz) using a Josephson parametric amplifier. As a milestone in this effort we have demonstrated 4-K thermal noise squeezing at 19 GHz. A superconductor–insulator–superconductor (SIS) mixer was employed as the detector. The parametric amplifier and SIS mixer were both cooled to 4.2 K, and care was taken using cold attenuators and isolators to make negligible the amount of room-temperature microwave noise coupled into the cryostat.
We are engaged in an experimental effort to generate and detect squeezed vacuum fluctuations at microwave frequencies using a Josephson parametric amplifier. We have demonstrated 42% deamplification of 4.2-K thermal noise at 19.4 GHz. At this frequency the vacuum fluctuation noise is an order of magnitude smaller than 4.2-K thermal noise. We have installed cryogenic HEMT amplifiers in our apparatus, thereby increasing the detector sensitivity by an order of magnitude. Josephson parametric amplifiers have been notorious for exhibiting excess noise whose origin is still controversial. We have performed a systematic study of the noise performance of our device both below and above threshold in a variety of modes of operation. The experiments indicate that the excess noise in our device arises from low-frequency noise (0-20 MHz) propagating down dc bias lines. When an intense coherent oscillation is present in the signal passband, such as the pump when the amplifier is in the four-photon mode or the period doubled oscillations when the amplifier is operated in the three-photon mode above threshold, the low- frequency noise mixes with the coherent oscillation to generate noise sidebands in the amplifier's passband. Nevertheless, in suitable conditions, extremely low noise and high gains were achieved.
Experiments on generating squeezed microwave radiation at 19.16 GHz using a Josephson parametric amplifier were performed. The source of the radiation was cooled by a dilution refrigerator down to the lowest temperature of 0.030 K. At this temperature, noise at the input port of the parametric amplifier consists almost entirely of the vacuum fluctuations with a noise temperature h nu /2k of 0.46 K. The authors observed the squeezing of the microwave noise by 47+or-8% as referred to the input of the Josephson parametric amplifier. The measured double-sideband noise temperature of the amplifier is 0.446 K, which is comparable to the vacuum noise level.
We report the observation of zero-point noise squeezing by means of a Josephson- junction parametric amplifier, which has been used previously to squeeze 4.2 K thermal noise1. To observe quantum noise squeezing, a number of improvements were made on the apparatus; these include the in stallation of two low-noise cryogenic high- electron-mobility-transistor (HEMT) amplifiers, which boosted the detector sensitivity an order of magnitude to 215 K. The Josephson- junction parametric amplifier was cooled to 30 mK and was operated in the degenerate mode with the signal carrier frequency at 19.16 GHz. At this frequency the vacuum noise floor is hv/2k = 0.46 K. In the deamplified quadrature a drop in the noise of 0.223 K was observed relative to the pump-off noise floor. The pump-off noise floor was established to be within 3.4 + 2.0% of the vacuum noise floor by varying the temperature of the cold termination at the parametric amplifier's input from 30 mK to 1K. A probe signal at the input of the first HEMT amplifier was used to establish that the detector system saturation was less than 7 × 10−4 dB. We have thus observed squeezing 47% ± 8% below the vacuum noise floor.
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 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.