article published yes Aviv Karnieli author Charles Roques-Carmes author e2e68fc9-6505-11ef-a541-eb4e72cc3e82 Nicholas Rivera author Shanhui Fan author A central challenge in the emerging field of free-electron quantum optics is to achieve strong quantum interaction and single-photon nonlinearity between a flying free electron and a photonic mode. Existing schemes are intrinsically limited by electron diffraction, which puts an upper bound on the interaction length and, therefore, on the strength of quantum coupling and nonlinearity. Here, we propose “free-electron fibers”: effectively one-dimensional photonic systems where free electrons copropagate with two guided modes. The first mode applies a ponderomotive trap to the free electron, removing the limitations due to electron diffraction. The second mode strongly couples to the guided free electron with an enhanced coupling that is orders of magnitude larger than previous designs. The extended interaction lengths enabled by our scheme allow for strong single-photon nonlinearities mediated by free electrons. We predict novel quantum effects in our system such as deterministic single-photon emission and nonlinear multimode dynamics. Our proposal paves the way toward the realization of heralded macroscopic nonclassical light generation, deterministic single-photon sources, and quantum gates controlled by free-electron–photon interactions. American Chemical Society2024 eng quantum opticsfree electronssingle photon nonlinearityelectron-photon interaction 2330-4022 2403.1307110.1021/acsphotonics.4c00908 1183401-3411 yes Karnieli, A., Roques-Carmes, C., Rivera, N., &#38; Fan, S. (2024). Strong coupling and single-photon nonlinearity in free-electron quantum optics. <i>ACS Photonics</i>. American Chemical Society. <a href="https://doi.org/10.1021/acsphotonics.4c00908">https://doi.org/10.1021/acsphotonics.4c00908</a> Karnieli, Aviv, et al. “Strong Coupling and Single-Photon Nonlinearity in Free-Electron Quantum Optics.” <i>ACS Photonics</i>, vol. 11, no. 8, American Chemical Society, 2024, pp. 3401–11, doi:<a href="https://doi.org/10.1021/acsphotonics.4c00908">10.1021/acsphotonics.4c00908</a>. Karnieli A, Roques-Carmes C, Rivera N, Fan S. Strong coupling and single-photon nonlinearity in free-electron quantum optics. <i>ACS Photonics</i>. 2024;11(8):3401-3411. doi:<a href="https://doi.org/10.1021/acsphotonics.4c00908">10.1021/acsphotonics.4c00908</a> A. Karnieli, C. Roques-Carmes, N. Rivera, S. Fan, ACS Photonics 11 (2024) 3401–3411. A. Karnieli, C. Roques-Carmes, N. Rivera, and S. Fan, “Strong coupling and single-photon nonlinearity in free-electron quantum optics,” <i>ACS Photonics</i>, vol. 11, no. 8. American Chemical Society, pp. 3401–3411, 2024. Karnieli A, Roques-Carmes C, Rivera N, Fan S. 2024. Strong coupling and single-photon nonlinearity in free-electron quantum optics. ACS Photonics. 11(8), 3401–3411. Karnieli, Aviv, Charles Roques-Carmes, Nicholas Rivera, and Shanhui Fan. “Strong Coupling and Single-Photon Nonlinearity in Free-Electron Quantum Optics.” <i>ACS Photonics</i>. American Chemical Society, 2024. <a href="https://doi.org/10.1021/acsphotonics.4c00908">https://doi.org/10.1021/acsphotonics.4c00908</a>. 215292026-03-30T12:22:47Z2026-04-27T10:30:37Z