Squeezing with a flux-driven Josephson parametric amplifier

Abstract

Josephson parametric amplifiers (JPA) are promising devices for applications\nin circuit quantum electrodynamics (QED) and for studies on propagating quantum\nmicrowaves because of their good noise performance. In this work, we present a\nsystematic characterization of a flux-driven JPA at millikelvin temperatures.\nIn particular, we study in detail its squeezing properties by two different\ndetection techniques. With the homodyne setup, we observe squeezing of vacuum\nfluctuations by superposing signal and idler bands. For a quantitative analysis\nwe apply dual-path cross-correlation techniques to reconstruct the Wigner\nfunctions of various squeezed vacuum and thermal states. At 10 dB signal gain,\nwe find 4.9+-0.2 dB squeezing below vacuum. In addition, we discuss the physics\nbehind squeezed coherent microwave fields. Finally, we analyze the JPA noise\ntemperature in the degenerate mode and find a value smaller than the standard\nquantum limit for phase-insensitive amplifiers.\n