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Physical Review Letters

Observation of zero-point noise squeezing via a Josephson-parametric amplifier

Roman Movshovich, Bernard Yurke, P. G. Kaminsky, A. D. Smith, Arnold H. Silver, R. W. Simon, Martin V. Schneider

Published Sep 17, 1990• 148 citations
Publisher

Abstract

We have demonstrated (47\ifmmode\pm\else\textpm\fi{}8)% squeezing of vacuum-fluctuation noise using a Josephson-parametric amplifier operated at 19.16 GHz. The amplifier was operated at 30 mK and has a double-sideband noise temperature of 0.446 K. This is comparable to the vacuum noise floor h\ensuremath{\nu}/2k=0.460 K.
DOI
10.1103/physrevlett.65.1419

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The authors observed the squeezing of 4.2 K thermal noise using a Josephson parametric amplifier operated in the degenerate mode at 19.4 GHz. A 42% reduction in the equilibrium noise was observed. The amplifier has also been operated at 0.1 K with an excess noise of 0.28 K referred to the amplifier's input port. This is less than the vacuum fluctuation noise of 0.47 K at the amplifier's input. Recently the amplifier has been operated in a nonchaotic mode with a signal gain in excess of 16 dB.>

IEEE Transactions on Magnetics•Mar 1, 1989•10 citations
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.
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.
The authors observed the squeezing of 4.2 K thermal noise using a Josephson parametric amplifier operated in the degenerate mode at 19.4 GHz. A 42% reduction in the equilibrium noise was observed. The amplifier has also been operated at 0.1 K with an excess noise of 0.28 K referred to the amplifier's input port. This is less than the vacuum fluctuation noise of 0.47 K at the amplifier's input. Recently the amplifier has been operated in a nonchaotic mode with a signal gain in excess of 16 dB.>