Entanglement in Resonance Fluorescence

TL;DR

This paper introduces a new method for generating entangled photon pairs using resonance fluorescence from a driven two-level system, offering tunable frequencies and optimized entanglement, with applications demonstrated in polariton systems.

Contribution

The authors present a novel entangled photon source based on resonance fluorescence, overcoming frequency matching limitations of traditional methods and enabling optimized entanglement for various applications.

Findings

Photon pairs are generated as superpositions of vacuum and Bell states.

The entanglement degree can be optimized for different frequencies.

Polariton systems can be driven into maximally entangled steady states.

Abstract

Particle entanglement is a fundamental resource upon which are based many quantum technologies. However, the up-to-now best sources of entangled photons rely on parametric down-conversion processes, which are optimal only at certain frequencies, which rarely match the energies of condensed-matter systems that can benefit from entanglement. In this Article, we show a way to circumvent this issue, and we introduce a new source of entangled photons based on resonance fluorescence delivering photon pairs as a superposition of vacuum and the Bell state $|\Phi^-\rangle$. Our proposal relies on the emission from the satellite peaks of a two-level system driven by a strong off-resonant laser, whose intensity controls the frequencies of the entangled photons. Furthermore, the degree of entanglement can be optimized for every pair of frequencies, thus demonstrating a clear advantage over existing technologies. Finally, we illustrate the power of our novel source of entangled single-photon pairs by exciting a system of polaritons and showing that they are left in a maximally entangled steady state.