  Silicon T centers present the promising possibility to generate optically
active spin qubits in an all-silicon device. However, these color centers
exhibit long excited state lifetimes and a low Debye-Waller factor, making them
dim emitters with low efficiency into the zero-phonon line. Nanophotonic
cavities can solve this problem by enhancing radiative emission into the
zero-phonon line through the Purcell effect. In this work we demonstrate
cavity-enhanced emission from a single T center in a nanophotonic cavity. We
achieve a two-orders of magnitude increase in brightness of the zero-phonon
line relative to waveguide-coupled emitters, a 23% collection efficiency from
emitter to fiber, and an overall emission efficiency into the zero-phonon line
of 63.4%. We also observe a lifetime enhancement of 5, corresponding to a
Purcell factor exceeding 18 when correcting for the emission to the phonon
sideband. These results pave the way towards efficient spin-photon interfaces
in silicon photonics.
