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arXiv:1711.02786 · Physical Review Applied

Optimal Operation of a Josephson Parametric Amplifier for Vacuum Squeezing

M. Malnou, Daniel Palken, Leila R. Vale, Gene C. Hilton, Konrad W. Lehnert

Published Apr 17, 2018• 64 citations
arXivHTMLPDF

Abstract

``Squeezed'' states of the microwave field, which allow one to beat the Heisenberg uncertainty limit for some phase values, find diverse applications in improving quantum measurements. These states can be created using a Josephson parametric amplifier (JPA) operated with a single current pump, but nonlinearities limit the available squeezing. The authors show how to choose pump-tone parameters to reduce this distortion, so that anyone with such a JPA can squeeze harder for better measurements, without needing extra hardware or a more complicated scheme.

DOI
10.1103/physrevapplied.9.044023

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``Squeezed'' states of the microwave field, which allow one to beat the Heisenberg uncertainty limit for some phase values, find diverse applications in improving quantum measurements. These states can be created using a Josephson parametric amplifier (JPA) operated with a single current pump, but nonlinearities limit the available squeezing. The authors show how to choose pump-tone parameters to reduce this distortion, so that anyone with such a JPA can squeeze harder for better measurements, without needing extra hardware or a more complicated scheme.
Josephson parametric amplifiers (JPA) are promising devices for applications in circuit quantum electrodynamics and for studies on propagating quantum microwaves because of their good noise performance. In this work, we present a systematic characterization of a flux-driven JPA at millikelvin temperatures. In particular, we study in detail its squeezing properties by two different detection techniques. With the homodyne setup, we observe the squeezing of vacuum fluctuations by superposing signal and idler bands. For a quantitative analysis, we apply dual-path cross-correlation techniques to reconstruct the Wigner functions of various squeezed vacuum and thermal states. At 10 dB signal gain, we find 4.9 ± 0.2 dB squeezing below the vacuum. In addition, we discuss the physics behind squeezed coherent microwave fields. Finally, we analyze the JPA noise temperature in the degenerate mode and find a value smaller than the standard quantum limit for phase-insensitive amplifiers.
Josephson parametric amplifiers (JPA) are nonlinear devices that are used for quantum sensing and qubit readout in the microwave regime. While JPAs regularly operate near the quantum limit, their gain saturates for very small (few-photon) input power. In a previous work, we showed that the saturation power of JPAs is not limited by pump depletion, but instead by the fourth-order nonlinearity of Josephson junctions, the nonlinear circuit elements that enables amplification in JPAs. Here, we present a systematic study of the nonlinearities in JPAs, show which nonlinearities limit the saturation power, and present a strategy for optimizing the circuit parameters for achieving the best possible JPA. For concreteness, we focus on JPAs that are constructed around a Josephson ring modulator (JRM). We show that by tuning the external and shunt inductors, we should be able to take the best experimentally available JPAs and improve their saturation power by $\ensuremath{\approx}15\phantom{\rule{0.16em}{0ex}}\mathrm{dB}$. Finally, we argue that our methods and qualitative results are applicable to a broad range of cavity-based JPAs.
The creation of high-quality cluster states in superconducting microwave circuits is a relevant ingredient in continuous-variable quantum computing. Although large-scale cluster states have been established in optical systems, dissipation prevents their direct applicability to the microwave realm. Recent improvements in superconducting parametric circuits, in particular Josephson parametric amplifiers (JPA) and traveling wave parametric amplifiers (TWPA), have permitted substantial progress in producing entangled states using microwave photons. In this paper, we examine experimentally and theoretically the effects of numerous parametric pump tones on the degree of two-mode squeezing in a quantum circuit and apply it to the JPA. We find that additional pumps diminish the initial two-mode correlations achieved with a single pump by redistributing it among a larger network of modes and by introducing entanglement with additional idler frequencies. Taking into account the actual heterodyne measurement conditions, the experimental results are consistent with theoretical expectations.
In quantum information processing, the Josephson parametric amplifier (JPA) has become a crucial tool for fast, high-fidelity readout of superconducting qubits, and for the generation of squeezed microwave radiation. However, research groups worldwide have reported unexpected nonidealities in these devices, leading to poorer than anticipated performance. Using numerical simulations complemented by experiments, the authors pinpoint oft-neglected higher-order circuit nonlinearities as the main source of these nonidealities, and provide simple, concrete steps to improve JPA performance.
Josephson parameter amplifier (JPA) is a microwave signal amplifier device with near-quantum-limit-noise performance. It has important applications in scientific research fields such as quantum computing and dark matter detection. This work reports the fabrication and characterization of broadband JPA devices and their applications in multi-qubit readout and squeezing of vacuum state. We use a process in which transmission lines and electrodes are made of niobium thin film and aluminum Josephson junctions are made by Dolan bridge technique. We believe this process is more convenient than the process we used previously. The whole production process adopts electron beam lithography technology to ensure high structural resolution. The test result shows that the gain value of the manufactured JPA can exceed 15 dB, and the amplification bandwidth is about 400 MHz. The noise temperature is about 400 mK at the working frequency of 6.2 GHz. The devices have been successfully used in experiments involving superconducting multi-qubit quantum processors. Furthermore, the device is applied to squeeze vacuum fluctuations and a squeezing level of 1.635 dB is achieved.