  Nanoscale control over the second-order photon correlation function
$g^{(2)}(\tau)$ is critical to emerging research in nonlinear nanophotonics and
integrated quantum information science. Here we report on quasiparticle control
of photon bunching with $g^{(2)}(0)>45$ in the cathodoluminescence of
nanodiamond nitrogen vacancy (NV$^0$) centers excited by a converged electron
beam in an aberration-corrected scanning transmission electron microscope.
Plasmon-mediated NV$^0$ cathodoluminescence exhibits a 16-fold increase in
luminescence intensity correlated with a three fold reduction in photon
bunching compared with that of uncoupled NV$^0$ centers. This effect is
ascribed to the excitation of single temporally uncorrelated NV$^0$ centers by
single surface plasmon polaritons. Spectrally resolved Hanbury Brown--Twiss
interferometry is employed to demonstrate that the bunching is mediated by the
NV$^0$ phonon sidebands, while no observable bunching is detected at the
zero-phonon line. The data are consistent with fast phonon-mediated
recombination dynamics, a conclusion substantiated by agreement between
Bayesian regression and Monte Carlo models of superthermal NV$^0$ luminescence.
