  We report the design, fabrication and optical investigation of electrically
tunable single quantum dot - photonic crystal defect nanocavities operating in
both the weak and strong coupling regimes of the light matter interaction.
Unlike previous studies where the dot-cavity spectral detuning was varied by
changing the lattice temperature, or by the adsorption of inert-gases at low
temperatures, we demonstrate that the quantum confined Stark effect can be
employed to quickly and reversibly switch the dot-cavity coupling simply by
varying a gate voltage. Our results show that exciton transitions from
individual dots can be tuned by ~4 meV relative to the nanocavity mode before
the emission quenches due to carrier tunneling escape. This range is much
larger than the typical linewidth of the high-Q cavity modes (~0.10 meV)
allowing us to explore and contrast regimes where the dots couple to the cavity
or decay by spontaneous emission into the 2D photonic bandgap. In the weak
coupling regime, we show that the dot spontaneous emission rate can be tuned
using a gate voltage, with Purcell factors >=7. New information is obtained on
the nature of the dot-cavity coupling in the weak coupling regime and
electrical control of zero dimensional polaritons is demonstrated for the
highest-Q cavities (Q>=12000). Vacuum Rabi splittings up to ~0.13 meV are
observed, much larger than the linewidths of either the decoupled exciton or
cavity mode. These observations represent a voltage switchable optical
non-linearity at the single photon level, paving the way towards on-chip dot
based nano-photonic devices that can be integrated with passive optical
components.
