Nonclassical states of light in systems with free electrons

Germaine Arend, Armin Feist, Jan-Wilke Henke +9 more

Nonclassical states of light, such as photon number states, are crucial in multiple regions of quantum technology. However, many states are still difficult to achieve. A potential new source of quantum states is free electron scattering. Especially coherent, parametric cathodoluminescence preserves the quantum phase between free electrons and light and enables wavelength tuning. Here, we demonstrate the generation of nonclassical multiphoton states via coherent cathodoluminescence, correlating electrons and photons in time and energy. We characterize the electron-heralded photons, observing the correlation between the electron energy loss and generated photon number and measuring an antibunching behavior in the electron-heralded optical intensity correlation. In the future, this combination of cathodoluminescence and correlation detection may form a versatile source of complex quantum photon states.

Javier Rivera-Dean

Mai Zhang, Yu Wang, Chang-Ling Zou +4 more

Harnessing a beam of slow free electrons in artificial photonic structures offers a powerful, tunable platform for generating nonclassical light 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 collective dynamics. When photon emission rate exceeds cavity losses, nonclassical lasing with sub-Poissonian photon statistics emerges, driven by multi-photon Rabi oscillations. At specific coupling strengths, 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.

Axel André

Songyu Zhu, Yushan Zeng, Chenhao Pan +3 more

The pursuit of programmable light sources with high coherence and spectral purity hinges on establishing a precise set of phase relationships in light-matter interactions. Here, we demonstrate that the quadratic dispersion of a freely propagating electron wave packet serves as a programmable quantum medium. Prepared in a coherent momentum-state ladder via a single laser interaction, the electron subsequently undergoes deterministic phase evolution during free propagation-an intrinsic process that compiles its quantum state into two distinct output channels. This mechanism, quantified by a quantum bunching factor, enables (i) Talbot-resonant bunching, where the electron density self-structures into subcycle combs with tunable harmonic selectivity, and (ii) coherent phase transfer of the programmed quadratic phase to light, generating nonclassical photon states such as multicomponent Schrödinger cat states via energy-resolved electron readout. This quadratic-phase programming provides a drift-section platform for Talbot-selected coherent short-wavelength emission and nonclassical light synthesis based on electron self-interference.

Klemens Hammerer, Claudiu Genes, David Vitali +4 more