Entangling microwaves with optical light

TL;DR

This paper demonstrates the creation and verification of entanglement between microwave and optical fields at millikelvin temperatures, enabling quantum communication between superconducting circuits and optical systems.

Contribution

It introduces a method to generate and verify microwave-optical entanglement using an optically pulsed superconducting electro-optical device, overcoming previous energy mismatch challenges.

Findings

Achieved microwave-optical entanglement with squeezing of 0.72 dB

Violated the Duan-Simon separability criterion by over 5 standard deviations

Established non-classical correlations between superconducting circuits and telecom light

Abstract

Entanglement is a genuine quantum mechanical property and the key resource in currently developed quantum technologies. Sharing this fragile property between superconducting microwave circuits and optical or atomic systems would enable new functionalities but has been hindered by the tremendous energy mismatch of $\sim10^5$ and the resulting mutually imposed loss and noise. In this work we create and verify entanglement between microwave and optical fields in a millikelvin environment. Using an optically pulsed superconducting electro-optical device, we deterministically prepare an itinerant microwave-optical state that is squeezed by $0.72^{+0.31}_{-0.25}$\,dB and violates the Duan-Simon separability criterion by $>5$ standard deviations. This establishes the long-sought non-classical correlations between superconducting circuits and telecom wavelength light with wide-ranging implications for hybrid quantum networks in the context of modularization, scaling, sensing and cross-platform verification.