  The efficiencies of photonic devices are primarily governed by radiative
quantum efficiency, which is a property given by the light emitting material.
Quantitative characterization for carbon nanotubes, however, has been difficult
despite being a prominent material for nanoscale photonics. Here we determine
the radiative quantum efficiency of bright excitons in carbon nanotubes by
modifying the exciton dynamics through cavity quantum electrodynamical effects.
Silicon photonic crystal nanobeam cavities are used to induce the Purcell
effect on individual carbon nanotubes. Spectral and temporal behavior of the
cavity enhancement is characterized by photoluminescence microscopy, and the
fraction of the radiative decay process is evaluated. We find that the
radiative quantum efficiency is near unity for bright excitons in carbon
nanotubes at room temperature.
