Continuous-wave electron-light interaction in high-Q whispering gallery microresonators

Achieving strong coupling of electron beams with single photons and harnessing their potential entanglement promises advancemenets in quantum optics with free-electron, merging spectroscopy of individual quantum systems with the nanoscale spatial resolution available in electron microscopes. Recent experiments on inelastic electron-light scattering (IELS) [1] , [2] with dielectric microcavities such as microspheres [3] or photonic crystal cavities [4] have demonstrated the potential of using resonant field enhancement for increasing the interaction between electrons and photons. IELS with continuous-wave (CW) excitation is, however, challenging due to transition probabilities normally being far below unity [5] .