Quantum sensing of electron beams using solid-state spins

TL;DR

This paper demonstrates the use of nitrogen-vacancy centers in diamond as quantum sensors to detect and analyze free-electron beams, establishing a foundation for hybrid quantum systems and nanoscale sensing.

Contribution

It introduces a theoretical and experimental framework for using NV- centers to sense free-electron beams, including a Lindblad master equation model and experimental validation.

Findings

Established an upper bound on electron-spin coupling strength.

Integrated fluorescence microscopy with electron beam for sensing.

Demonstrated NV- centers as quantitative probes of free electrons.

Abstract

Scattering experiments with energetic particles, such as free electrons, have been historically used to reveal the quantum structure of matter. However, realizing coherent interactions between free-electron beams and solid-state quantum systems has remained out of reach, owing to their intrinsically weak coupling. Realizing such coherent control would open up opportunities for hybrid quantum platforms combining free electrons and solid-state qubits for coincident quantum information processing and nanoscale sensing. Here, we present a framework that employs negatively charged nitrogen-vacancy centers (NV-) in diamond as quantum sensors of a bunched electron beam. We develop a Lindblad master equation description of the magnetic free-electron--qubit interactions and identify spin relaxometry as a sensitive probe of the interaction. Experimentally, we integrate a confocal fluorescence microscopy setup into a microwave-bunched electron beam line. We monitor charge-state dynamics and assess their impact on key sensing performance metrics (such as spin readout contrast), defining safe operating parameters for quantum sensing experiments. By performing $T_1$ relaxometry under controlled electron beam exposure, we establish an upper bound on the free-electron--spin coupling strength. Our results establish NV- centers as quantitative probes of free electrons, providing a metrological benchmark for free-electron--qubit coupling under realistic conditions, and chart a route toward solid-state quantum control with electron beams.