Quantum non-Gaussian Photon Coincidences

Photon coincidences represent an important resource for quantum technologies. They expose nonlinear quantum processes in matter and are essential for sources of entanglement. We derive broadly applicable criteria for quantum non-Gaussian two-photon coincidences that certify a new quality of photon sources. The criteria reject states emerging from Gaussian parametric processes, which often limit applications in quantum technologies. We also analyse the robustness of the quantum non-Gaussian coincidences and compare with the heralded quantum non-Gaussianity of single-photons based on them.