Quantum sensing and metrology with free electrons

TL;DR

This paper introduces a novel quantum sensing method using free electrons interacting with waveguided light, achieving higher sensitivity and generating high-photon-number states beyond traditional optical limits.

Contribution

It demonstrates a new approach combining free electrons and waveguided photons to enhance quantum sensing and generate high-photon-number states at high rates.

Findings

Tenfold increase in optical-phase sensitivity with current technology

Generation of waveguided NOON states with tens of photons at megahertz rates

Strong electron-light coupling via aloof electron reflection

Abstract

The quantum properties of matter and radiation can be leveraged to surpass classical limits of sensing and detection. Quantum optics does so by creating and measuring nonclassical light. However, better performance requires higher photon-number states, which are challenging to generate and detect. Here, we combine photons and free electrons to solve the problem of generating and detecting high-number states well beyond those reachable with light alone and further show that an unprecedented level of sensitivity and resolution is gained based on the measurement of free-electron currents after suitably designed electron-light interaction events. Our enabling ingredient is the strong electron-light coupling produced by aloof electron reflection on an optical waveguide, leading to the emission or absorption of a high number of guided photons by every single electron. We theoretically demonstrate that, by combining electron-beam splitters with two electron-waveguide interactions, the sensitivity to detect optical-phase changes can be enhanced tenfold using currently attainable technology. We further show that waveguided NOON states comprising tens of photons can be generated at megahertz rates based on electron post-selection after electron-waveguide interaction. These results inaugurate a disruptive quantum technology relying on free electrons and their strong interaction with waveguided light.