Electrons herald non-classical light

TL;DR

This paper demonstrates that free electrons can generate non-classical light states through quantum energy exchange, enabling heralded single-photon and multi-photon states for quantum optics applications.

Contribution

It introduces a method to produce and control non-classical light states using free-electron interactions, advancing quantum light source technology.

Findings

Electron energy loss correlates with photon number generation.

Single-electron energy loss heralds single-photon states.

Two-electron energy losses produce two-photon coincidences.

Abstract

Free electrons are a widespread and universal source of electromagnetic fields. The past decades witnessed ever-growing control over many aspects of electron-generated radiation, from the incoherent emission produced by X-ray tubes to the exceptional brilliance of free-electron lasers. Reduced to the elementary process of quantized energy exchange between individual electrons and the electromagnetic field, electron beams may facilitate future sources of tunable quantum light. However, the quantum features of such radiation are tied to the correlation of the particles, calling for the joint electronic and photonic state to be explored for further applications. Here, we demonstrate the coherent parametric generation of non-classical states of light by free electrons. We show that the quantized electron energy loss heralds the number of photons generated in a dielectric waveguide. In Hanbury-Brown-Twiss measurements, an electron-heralded single-photon state is revealed via antibunching intensity correlations, while two-quantum energy losses of individual electrons yield pronounced two-photon coincidences. The approach facilitates the tailored preparation of higher-number Fock and other optical quantum states based on controlled interactions with free-electron beams.