Electrical control of spontaneous emission and strong coupling for a single quantum dot

We report the design, fabrication and optical investigation of electrically tunable single quantum dots-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 (∼100 μeV) allowing us to explore and contrast regimes where the dots couple to the cavity or decay by spontaneous emission into the two-dimensional photonic bandgap. In the weak-coupling gime, 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 ≥ 12 000). Vacuum Rabi splittings up to ∼ 120 μeV are observed, larger than the linewidths of either the decoupled exciton (Γ ≤ 40 μeV) or cavity mode. These observations represent a voltage switchable optical nonlinearity at the single photon level, paving the way towards on-chip dot-based nano-photonic devices that can be integrated with passive optical components.