Fig. 4: Statistical analysis of generated photons.

a,b, N_e,A,B as a function of photon-electron time delays, selected by electron energy: m = 1 (a) and m = 2 (b). c, Violation of the Cauchy–Schwartz inequality (γ > 1) for the electron–photon interaction at different τ. d, Unheralded photon–photon intensity correlation for varying electron current. e, Electron-heralded photon–photon intensity correlation filtered to the energy region m = 1 as a function of both time delays. Inset: time-averaged g⁽²⁾ for m = 1. f, Photon–photon intensity correlation as a function of the number of photon-heralding electrons q between the two heralded photons without energy selection (top) and for m = 1 (bottom).