@article{21529,
  abstract     = {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.},
  author       = {Karnieli, Aviv and Roques-Carmes, Charles and Rivera, Nicholas and Fan, Shanhui},
  issn         = {2330-4022},
  journal      = {ACS Photonics},
  keywords     = {quantum optics, free electrons, single photon nonlinearity, electron-photon interaction},
  number       = {8},
  pages        = {3401--3411},
  publisher    = {American Chemical Society},
  title        = {{Strong coupling and single-photon nonlinearity in free-electron quantum optics}},
  doi          = {10.1021/acsphotonics.4c00908},
  volume       = {11},
  year         = {2024},
}

@article{21525,
  abstract     = {We present a novel design for an ultracompact, passive light source capable of generating ultraviolet and X-ray radiation, based on the interaction of free electrons with the magnetic near-field of a ferromagnet. Our design is motivated by recent advances in the fabrication of nanostructures, which allow the confinement of large magnetic fields at the surface of ferromagnetic nanogratings. Using ab initio simulations and a complementary analytical theory, we show that highly directional, tunable, monochromatic radiation at high frequencies could be produced from relatively low-energy electrons within a tabletop design. The output frequency is tunable in the extreme ultraviolet to hard X-ray range via electron kinetic energies from 1 keV to 5 MeV and nanograting periods from 1 μm to 5 nm. The proposed radiation source can achieve the tunability and monochromaticity of current free-electron-driven sources (free-electron lasers, synchrotrons, and laser-driven undulators), yet with a significantly reduced scale, cost, and complexity. Our design could help realize the next generation of tabletop or on-chip X-ray sources.},
  author       = {Fisher, Sophie and Roques-Carmes, Charles and Rivera, Nicholas and Wong, Liang Jie and Kaminer, Ido and Soljačić, Marin},
  issn         = {2330-4022},
  journal      = {ACS Photonics},
  keywords     = {X-ray sources, free electrons, nanostructure, undulator, synchrotron, free-electron laser},
  number       = {5},
  pages        = {1096--1103},
  publisher    = {American Chemical Society },
  title        = {{Monochromatic X-ray source based on scattering from a magnetic nanoundulator}},
  doi          = {10.1021/acsphotonics.0c00121},
  volume       = {7},
  year         = {2020},
}