Fig. 1: Correlation measurement of waveguide-coupled photons and free electrons.
a, A beam of electrons passes a dielectric waveguide, generating photons that are guided and detected in a fibre-based HBT set-up. The electron and photon arrival times are temporally correlated. b, Enlarged sketch of the interaction region: the electron passes the waveguide surface at an impact parameter of around 250 nm to interact with the evanescent vacuum field of the waveguide modes. c, Simulation of the photon spectral distribution generated in a 40-μm straight waveguide by 100-keV electrons (impact parameter 250 nm). Grey vertical lines: waveguide boundaries. a.u., arbitrary units. d, False-colour image of an example photonic chip (scanning electron micrograph). The chip surface is covered with ITO (indium tin oxide; brighter surface, ITO on metal; darker surface, ITO on Si3N4 or on SiO2; side walls, SiO2). e, Schematic of the correlated quantized electron energy loss and photon number. The electron scatters at the optical mode, generating a random number of photons. After detection, the signal correlation links the photon number k to the electron scattering order m. The generation process is expected to follow a Poissonian distribution.
