We report on the experimental demonstration of single photon state generation and characterization in an electron microscope. In this aim we have used low intensity relativistic (energy between 60kV and 100 keV) electrons beams focused in a ca 1 nm probe to excite diamond nanoparticles. This triggered individual neutral Nitrogen-vacancies (NV0) centers to emit photon which could be gathered and sent to a Hanbury Brown Twiss intensity interferometer. The detection of a dip in the correlation function at small time delays clearly demonstrates antibunching and thus the creation of non-classical light states. Specifically, we have also demonstrated single photon state detection. We unveil the mechanism behind quantum states generation in an electron microscope, and show that it clearly makes cathodoluminescence the nanometer scale analog of photoluminescence rather than electroluminescence. By using an extremely small electron probe size and the ability to monitor its position with sub nanometer resolution, we also show the possibility of measuring the quantum character of the emitted beam with deep sub wavelength resolution.
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