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Physical Review

Operation of a Solid-State Quantum-Mechanical Amplifier

M. W. P. Strandberg, C. F. Davis, Brian W. Faughnan, Robert L. Kyhl, G. J. Wolga

Published Mar 15, 1958• 20 citations
Publisher

Abstract

The operation of an $S$-band solid-state quantum-mechanical amplifier operated at 4.2\ifmmode^\circ\else\textdegree\fi{}K with a computed noise temperature of less than 4.5\ifmmode^\circ\else\textdegree\fi{}K is compared with similar devices and is used as proof of the condition of discrete phonon saturation which has been previously postulated.

DOI
10.1103/physrev.109.1988

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The operation of an SSS-band solid-state quantum-mechanical amplifier operated at 4.2\ifmmode^\circ\else\textdegree\fi{}K with a computed noise temperature of less than 4.5\ifmmode^\circ\else\textdegree\fi{}K is compared with similar devices and is used as proof of the condition of discrete phonon saturation which has been previously postulated.
Amplification of weak microwave signals with minimal added noise is of importance to science and technology. Artificial quantum systems, based on superconducting circuits, can now amplify and detect even single microwave photons. However, this requires operating at millikelvin temperatures. Natural quantum systems can also be used for low-noise microwave amplification using stimulated emission effects; however, they generate a higher noise, especially when operating above ~1 K. Here, we demonstrate the use of electron spins in diamond as a quantum microwave amplifier operating with quantum-limited internal noise, even above liquid nitrogen temperatures. We report on the amplifier's design, gain, bandwidth, saturation power, and noise. This capability can lead the way to previously unavailable quantum science, engineering, and physics applications.
Conventional amplifiers add quantum noise to a signal. Both amplifiers and attenuators lead to a reduction of the signal-to-noise ratio. We find, however, that devices exhibiting squeezed fluctuations in the gain or loss medium lead to an improved signal-to-noise ratio, in one quadrature of the output, compared to the limits associated with conventional devices. We investigate amplifier and attenuator noise properties using a simple model in which the gain or loss medium is a broad-band reservoir in a specially prepared, or ‘rigged’, state.
A microwave amplifier combining noise performances as close as possible to the quantum limit with large bandwidth and high saturation power is highly desirable for many solid-state quantum technologies.Here, we introduce a new traveling-wave parametric amplifier based on superconducting quantum interference devices.It displays a 3-GHz bandwidth, a -100-dBm saturation (1-dB compression) point and added noise near the quantum limit.Compared to the previous state of the art, it is an order of magnitude more compact, its characteristic impedance is in situ tunable, and its fabrication process requires only two lithography steps.The key is the engineering of a gap in the dispersion relation of the transmission line.This is obtained using a periodic modulation of the SQUID size, similarly to what is done with photonic crystals.Moreover, we provide a new theoretical treatment to describe the nontrivial interplay between nonlinearity and such periodicity.Our approach provides a path to cointegration with other quantum devices such as qubits given the low footprint and easy fabrication of our amplifier.
An expression is derived for the noise figure for a quantum-mechanical amplifier in terms of the physical quantities describing the electromagnetic structure and the paramagnetic salts---such as gain, circuit Q′sQ'\mathrm{s}Q′s, and salt molecular weight and volume.
The noise figure or limiting sensitivity for both traveling-wave and resonant-cavity quantum-mechanical amplifiers, sensitive to one direction of propagation, is derived with spontaneous emission as the limiting noise. The concept of effective temperature is introduced as an analytical parameter; thus negative temperatures appear in a natural fashion. It is pointed out that the results of this calculation can be considered the solution to the problem of linear counting of coherent particles. In this case the least count is one and the signal-to-noise ratio (for constant photon flux) increases as the reciprocal of the band width. The limiting temperature sensitivity of properly designed quantum-mechanical amplifiers is given as $\frac{h\ensuremath{\nu}}{k}$ degrees because of the drastic difference between negative and positive temperatures.