Tunable quantum light by modulated free electrons

TL;DR

This paper develops a theoretical framework to predict and control the quantum states of light generated by modulated free electrons, enabling the creation of high-purity, non-Gaussian, and tailored quantum light states for advanced quantum applications.

Contribution

It introduces a comprehensive theoretical model for electron-induced light states and demonstrates methods to generate various nonclassical states with high fidelity using electron modulation and filtering.

Findings

Coherent states with 90% purity can be formed via spectral pre-filtering.

Non-Gaussian states are generated through precise energy measurement.

Strategies to produce squeezed, cat, and triangular states with near-perfect fidelity.

Abstract

Nonclassical states of light are fundamental in various applications, spanning quantum computation to enhanced sensing. Fast free electrons, which emit light into photonic structures through the mechanism of spontaneous emission, represent a promising platform for generating diverse types of states. Indeed, the intrinsic connection between the input electron wave function and the output light field suggests that electron-shaping schemes, based on light-induced scattering, facilitates their synthesis. In this article, we present a theoretical framework capable of predicting the final optical density matrix of a generic N-electron state that can also account for post-sample energy filtering. By using such framework, we study the modulation-dependent fluctuations of the N-electron emission and identify regions of Poissonian and super-Poissonian statistics. In the single-electron case, we show how coherent states with nearly 90% purity can be formed by pre-filtering a portion of the spectrum after modulation, and how non-Gaussian states are generated after a precise energy measurement. Furthermore, we present a strategy combining a single-stage electron modulation and post-filtering to harness tailored light states, such as squeezed vacuum, cat, and triangular cat states, with fidelity close to 100%.