Squeezing with a flux-driven Josephson parametric amplifier

TL;DR

This paper systematically characterizes a flux-driven Josephson parametric amplifier at millikelvin temperatures, demonstrating significant vacuum squeezing and low noise performance suitable for quantum microwave applications.

Contribution

It provides a detailed experimental analysis of a flux-driven JPA's squeezing capabilities and noise properties, including dual detection techniques and Wigner function reconstruction.

Findings

Achieved 4.9 dB vacuum squeezing at 10 dB gain

Demonstrated noise temperature below the standard quantum limit

Used dual-path cross-correlation for state reconstruction

Abstract

Josephson parametric amplifiers (JPA) are promising devices for applications in circuit quantum electrodynamics (QED) 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 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 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.