Two-colour high-purity Einstein-Podolsky-Rosen photonic state

TL;DR

This paper demonstrates a high-purity, two-colour EPR entangled state of light with over 200 nm wavelength separation, enabling advanced quantum communication and sensing applications across a broad frequency range.

Contribution

It introduces a novel method to generate high-purity, two-colour entangled light modes with significant wavelength separation, suitable for quantum networks and interfaces.

Findings

Achieved -7.7 dB of two-mode entanglement.

State purity of 0.63±0.16.

Entanglement observed over five octaves of frequencies.

Abstract

Entanglement is the backbone of quantum information science and its applications. Entangled states of light are necessary for distributed quantum protocols, quantum sensing and quantum internet. A distributed quantum network requires entanglement between light modes of different colours optimized for interaction with the nodes as well as for communication between them. Here we demonstrate a high-purity Einstein-Podolsky-Rosen (EPR) entangled state between light modes with the wavelengths separated by more than 200 nm. The modes display $-7.7\pm0.5$ dB of two-mode entanglement and an overall state purity of $0.63\pm0.16$. Entanglement is observed over five octaves of sideband frequencies from rf down to audio-band. In the context of two-colour entanglement, the demonstrated combination of high state purity, strong entanglement, and extended frequency range paves the way to new matter-light quantum protocols, such as teleportation between disparate quantum systems, quantum sensing and quantum-enhanced gravitational wave interferometry. The scheme demonstrated here can be readily applied towards entanglement between telecom wavelengths and atomic quantum memories.