Quantum optics with free electrons: from quantum sensing to strong coupling and single-photon nonlinearity (Invited Paper)

Free electrons are an emerging new type of quantum probe, with high quantum coherence, sub fsec – sub-nm resolution, high tunability and pristine coherent control. Recent experimental and theoretical advancements showcased the quantum nature of the interaction between a free electron and light and bound-electron qubits, with demonstrations of strong electron-photon coupling and coincidence, and proposals for quantum light generation.