Low-Energy Free-Electron Nonclassical Lasing

Harnessing a beam of slow free electrons in artificial photonic structures offers a tunable platform for studying quantum optics without the need for heavy physical equipment. Here, we present a theory of nonclassical lasing, demonstrating how incoherent electrons in photonic crystal cavities can coherently emit photons through electronic collective dynamics. When the photon emission rate exceeds cavity losses, nonclassical lasing with sub-Poissonian photon statistics emerges, driven by multiphoton Rabi oscillations. At specific coupling strengths, the quantum state trapping effect emerges, producing high-fidelity Fock states at room temperature (e.g., nearly 90% fidelity of four-photon Fock state). Notably, the frequency of the emitted photons can be readily tuned via the velocity of the injected electrons to match cavity modes. This approach supports photonic integration and offers a scalable, energy-efficient platform for room-temperature quantum light sources and advanced studies in quantum electrodynamics.