  Impurity-vacancy centers in diamond offer a new class of robust photon
sources with versatile quantum properties. While individual color centers
commonly act as single-photon sources, their ensembles have been theoretically
predicted to have tunable photon-emission statistics. Importantly, the
particular type of excitation affects the emission properties of a color center
ensemble within a diamond crystal. While optical excitation favors
non-synchronized excitation of color centers within an ensemble, electron-beam
excitation can synchronize the emitters and thereby provides a control of the
second-order correlation function $g_2(0)$. In this letter, we demonstrate
experimentally that the photon stream from an ensemble of color centers can
exhibit $g_2(0)$ both above and below unity. Such a photon source based on an
ensemble of few color centers in a diamond crystal provides a highly tunable
platform for informational technologies operating at room temperature.
