Quantum microwave parametric interferometer

TL;DR

This paper reports the experimental development of a quantum microwave interferometer using Josephson amplifiers, demonstrating its ability to surpass classical limits and exhibit non-classical photon statistics for enhanced quantum measurements.

Contribution

It introduces a novel superconducting Josephson interferometer operating in the microwave regime, with systematic analysis showing quantum advantages over classical interferometers.

Findings

Gaussian interferometric power exceeds shot-noise limit

Output modes show sub-Poissonian photon statistics

Low-gain regime identified as optimal for quantum illumination

Abstract

Classical interferometers are indispensable tools for the precise determination of various physical quantities. Their accuracy is bound by the standard quantum limit. This limit can be overcome by using quantum states or nonlinear quantum elements. Here, we present the experimental study of a nonlinear Josephson interferometer operating in the microwave regime. Our quantum microwave parametric interferometer (QUMPI) is based on superconducting flux-driven Josephson parametric amplifiers combined with linear microwave elements. We perform a systematic analysis of the implemented QUMPI. We find that its Gaussian interferometric power exceeds the shot-noise limit and observe sub-Poissonian photon statistics in the output modes. Furthermore, we identify a low-gain operation regime of the QUMPI which is essential for optimal quantum measurements in quantum illumination protocols.