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Observation of parametric deamplification in a Josephson parametric amplifier

Bernard Yurke, P. G. Kaminsky, L. W. JUN. RUPP, Edward A. Whittaker, A. D. Smith, Arnold H. Silver, R. W. Simon

Published Apr 26, 1987• 1 citation
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Abstract

The successful generation and detection of squeezed electromagnetic radiation at optical frequencies1 promise to open the door to the exploration of new quantum phenomena, some of which may be technologically useful.2 The generation and detection of squeezed radiation at low frequencies would also open the door to the observation of novel quantum phenomena. We report here on a Josephson parametric amplifier which appears to be well behaved and may be suitable for generating squeezed coherent microwave radiation. The amplifier was operated in the four-photon or doubly degenerate mode,3 and thus its operation is akin to that of an optical four-wave mixer.1

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The successful generation and detection of squeezed electromagnetic radiation at optical frequencies1 promise to open the door to the exploration of new quantum phenomena, some of which may be technologically useful.2 The generation and detection of squeezed radiation at low frequencies would also open the door to the observation of novel quantum phenomena. We report here on a Josephson parametric amplifier which appears to be well behaved and may be suitable for generating squeezed coherent microwave radiation. The amplifier was operated in the four-photon or doubly degenerate mode,3 and thus its operation is akin to that of an optical four-wave mixer.1
We present the results of an experimental effort to generate squeezed microwave radiation using the phase-sensitive gain of a Josephson parametric amplifier. To facilitate the interpretation of the experimental results, we first present a discussion of the theory of microwave squeezing via Josephson parametric amplifiers. This is followed by a detailed description of the device fabricated for our experiment. Experimental results are then presented for the device used in both the doubly degenerate or four-photon mode and for the degenerate or three-photon mode. We have observed parametric deamplification of signals by more than 8 dB. We have demonstrated squeezing of 4.2-K thermal noise. When operated at 0.1 K, the amplifier exhibits an excess noise of 0.28 K when referred to the input. This is smaller than the vacuum fluctuation noise level \ensuremath{\Elzxh}\ensuremath{\omega}/2k=0.47 K. The amplifier is thus quieter than a linear phase-insensitive amplifier in principle can be.
Josephson traveling wave parametric amplifiers have enabled ultra-sensitive detection of microwave photons in radio astronomy and real-time readout of superconducting quantum bits. To achieve a large gain, the interaction time with the non-linearity of the amplifier needs to be maximized. Traveling wave parametric amplifiers exhibit long interaction times by providing long propagation paths, enabling a greater gain and higher bandwidths than other microwave parametric amplifiers. In the case of the degenerate Josephson parametric amplifier (DJPA) below threshold of parametric oscillation, a squeezed vacuum state can be generated, and above threshold a second bifurcation point exists, where the device generates amplitude squeezed radiation.
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.
A squeezed state of the electromagnetic field has less noise in one of its two amplitude components than that of a coherent state. This property makes squeezed states potentially useful in low noise and precision measurement. Squeezed states may be generated by, among other things, degenerate parametric amplifiers and four-wave mixers. The reduced noise in one of the amplitude components is most easily observed via a homodyne detector. A number of experimental efforts to generate and detect squeezed states are under way. Here, in describing experimental techniques, the experiments' carried out by Slusher et al. are emphasized. A number of techniques were employed to successfully generate squeezed light. An atomic beam of sodium provided the optical nonlinearity in a cavity-backward four-wave mixer. By employing pairs of Fabry-Perot modes spaced symmetrically about the pump frequency, squeezed light was generated in nondegenerate conditions where Rayleigh scattering of pump light could be avoided. To observe squeezing, a number of nonidealities such as phase jitter and detector inefficiencies also had to be overcome.
Degenerate parametric amplifiers (DPAs) exhibit the unique property of phase-sensitive gain and can be used to noiselessly amplify small signals or squeeze field fluctuations beneath the vacuum level. In the microwave domain, these amplifiers have been utilized to measure qubits in elementary quantum processors, search for dark matter, facilitate high-sensitivity spin resonance spectroscopy and have even been proposed as the building blocks for a measurement based quantum computer. Until now, microwave DPAs have almost exclusively been made from nonlinear Josephson junctions, which exhibit high-order nonlinearities that limit their dynamic range and squeezing potential. In this work we investigate a new microwave DPA that exploits a nonlinearity engineered from kinetic inductance. The device has a simple design and displays a dynamic range that is four orders of magnitude greater than state-of-the-art Josephson DPAs. We measure phase sensitive gains up to 50 dB and demonstrate a near-quantum-limited noise performance. Additionally, we show that the higher-order nonlinearities that limit other microwave DPAs are almost non-existent for this amplifier, which allows us to demonstrate its exceptional squeezing potential by measuring the deamplification of coherent states by as much as 26 dB.