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IEEE Transactions on Magnetics

SQUID parametric amplifier

Arnold H. Silver, Robert D. Sandell, John P. Hurrell, David C. Pridmore-Brown

Published May 1, 1983• 4 citations
Publisher

Abstract

The single junction SQUID was previously shown by analysis and simulation to be an attractive candidate for a parametric amplifier. Further calculations of the noise and saturation behavior of the nearly degenerate parametric amplifier have now been performed by numerical simulation. These simulations clearly show that the amplifier noise temperature will be approximately the device temperature T0, and that the amplifier will be completely saturated in the presence of white noise characteristic of 30T0. Signal saturation of the amplifier also occurs for an output power10^{-2}F_{o}\phi_{o}^{2}/2L, strongly limiting the dynamic range, However, a coherent array of N single junction SQUIDs is shown to have a signal saturation level increased by N relative to a single SQUID, with no increase in noise temperature, resulting in an N-fold improvement in dynamic range.

DOI
10.1109/tmag.1983.1062473

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The single junction SQUID was previously shown by analysis and simulation to be an attractive candidate for a parametric amplifier. Further calculations of the noise and saturation behavior of the nearly degenerate parametric amplifier have now been performed by numerical simulation. These simulations clearly show that the amplifier noise temperature will be approximately the device temperature T0, and that the amplifier will be completely saturated in the presence of white noise characteristic of 30T0. Signal saturation of the amplifier also occurs for an output power10^{-2}F_{o}\phi_{o}^{2}/2L, strongly limiting the dynamic range, However, a coherent array of N single junction SQUIDs is shown to have a signal saturation level increased by N relative to a single SQUID, with no increase in noise temperature, resulting in an N-fold improvement in dynamic range.
This is the first Annual Report of an effort to demonstrate a low noise superconducting microwave amplifier. The amplifier is a nearly degenerate, single idler parametric amplifier which uses the nonlinear inductance of a single junction SQUID (Superconducting Quantum Interference Device). The design frequency is 9 GHz, 10 dB gain, and 16% bandwidth. In order to maximize the saturation power, the device impedance was chosen near 1ohm and a matching network was designed to transform to 50ohm. In later designs, a coherent array of SQUIDs is expected to increase the power and impedance. This report includes the design and test of the 50ohm to 1ohm broadband transformer, design and fabrication of the SQUID amplifier, and both saturation and noise analyses of the single SQUID and SQUID array. The analytical results, reported to the 1982 Applied Superconductivity Conference are: the noise temperature of the single SQUID parametric amplifier is equal to the amplifier termination temperature T(o), the response is linear to several percent of the flux quantum energy in the SQUID: the amplifier will be saturated by broad band noise if the noise source temperature is much greater than 10 To; and the array parametric amplifier has the same noise temperature as the single device indicating an N-fold increase in dynamic range. (Author)
We report the lowest noise temperature of any microwave amplifier except the maser. This amplifier is a nearly degenerate superconducting parametric amplifier at X-band consisting of a low β, thin film, single junction SQUID, a monolithic 50 Ω to 1 Ω impedance matching network, and a cooled circulator. Nb/Nb2O5/Pb alloy junctions were incorporated into Nb and Pb-in circuitry on 1×2 cm silicon chips. The SQUID was phase-biased near 90° and driven by an external pump at approximately twice the operating frequency. The self-resonance frequency of the SQUID inductance and junction capacitance was set at the operating frequency of 8.2GHz. The operating charac teristics depended on the pump amplitude, the junction phase bias, and the SQUID parameters. For small values of\beta < 1, the maximum gain in both the signal and idler channels was ≈10dB, the bandwidth = 170MHz, and the single-sidehand noise temperature was 6K with an uncertainty of (+15 to -7)K. For higher β, the gain increased to nearly 30dB with increased noise and parametric oscillations occurring near the pump subharmonic frequency.
TRW has been developing low noise microwave parametric amplifier with Josephson junction SQUIDs (Superconducting Quantum Interference Devices). This report summarizes the second phase of the program which includes measurement of the amplifier performance at X-band, and design and fabrication of a SQUID array amplifier. We have demonstrated gain in excess of 10 dB at 8.4 GHz and a measured noise temperature equal to 6K with an uncertainty of (+15/-7)K. Arrays with both 25 and 50 elements and 50 ohmi impedance have been designed and fabricated. These arrays should increase the dynamic range of the amplifier.
Josephson parametric amplifiers (JPAs) are key devices in superconducting quantum circuits, as they ultimately dictate quantum efficiency and speed of measurement, but they still suffer from low saturation power. This work shows that a JPA's saturation power can be increased by using a Josephson-junction array, rather than a single-junction amplifier. Modeling such an array as a nonlinear $L\phantom{\rule{0}{0ex}}C$ resonator reproduces the observed amplification and saturation effects very well. This use of arrays to fight low power saturation is easy to implement, and can be directly combined with impedance-engineered environments to enhance dynamic range even more.
Josephson junctions incorporated into microcircuit SQUIDs have many uses including digital logic and memory, parametric amplification, signal generation, and analog to digital conversion. Combining SQUIDs into coherent arrays can preserve these functions and add great flexibility in selecting power and impedance. We have investigated such general properties of the SQUID lattice array as the mode structure, dispersion relations, and stability. In particular, one unique antisymmetric mode is shown to precisely reproduce the performance of a single rf SQUID, with increased power and impedance. The application of this mode to parametric amplification has been demonstrated analytically and numerically, projecting a useful low noise amplifier with a gain of 10dB at 16% bandwidth.
We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.