Strong coupling and single-photon nonlinearity in free-electron quantum optics Karnieli, Aviv Roques-Carmes, Charles Rivera, Nicholas Fan, Shanhui quantum optics free electrons single photon nonlinearity electron-photon interaction ddc:530 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 Society 2024 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/21529 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> eng info:eu-repo/semantics/altIdentifier/doi/10.1021/acsphotonics.4c00908 info:eu-repo/semantics/altIdentifier/e-issn/2330-4022 info:eu-repo/semantics/altIdentifier/arxiv/2403.13071 info:eu-repo/semantics/openAccess