Electrically tunable single-dot nanocavities in the weak and strong coupling regimes

We report the design, fabrication and optical investigation of electrically tunable single quantum dot - photonic crystal defect nanocavities [1] 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 [2,3], or by the adsorption of inert-gases at low temperatures [4], 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 [1]. Our results show that exciton transitions from individual dots can be tuned by up to ~4meV relative to the nanocavity mode, before the emission quenches due to carrier tunnelling escape from the dots. This range is much larger than the typical linewidth of the high-Q cavity modes (κ=116μeV), allowing us to explore and contrast regimes where the dots couple to an optical cavity or decay by spontaneous emission into the 2D photonic bandgap. By performing CW and time resolved confocal microscopy at a fixed sample temperature (10K) we directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. 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 first time. Vacuum Rabi splittings up to 2g~120μeV are observed for the highest-Q cavities with Q~10500, much larger than the linewidths of either the decoupled exciton (γ30 linewidths. The devices fabricated allow studies of cavity-QED phenomena in a system that can be tuned in-situ, at low temperatures. Furthermore, prospects for direct electrical readout of the strongly coupled dot-cavity system using photocurrent methods will be discussed. This work is financially supported by the DFG via SFB 631 and by the German Excellence Initiative via the “Nanosystems Initiative Munich (NIM)”.