Dephasing of Exciton Polaritons in Photoexcited InGaAs Quantum Dots in GaAs Nanocavities

We present a combined experimental and theoretical study of the emission spectrum of zero dimensional nanocavity polaritons in electrically tunable single dot nanocavities. Such devices allow us to vary the dot-cavity detuning in situ and probe the emission spectrum under well-controlled conditions of lattice temperature and incoherent excitation level. Our results show that the observation of a double peak in the emission spectrum is not an unequivocal signature of strong coupling. Moreover, by comparing our results with theory, we extract the effective vacuum Rabi splitting, the pure dephasing rate, and their dependence on the incoherent optical pumping power and lattice temperature. Our study highlights how coupling to the lattice and dynamical fluctuations in the solid-state environment influence the coherence properties of quantum dot microcavity polaritons and, sometimes, may mask the occurrence of strong coupling.

Figure 1

(left panel) Waterfall plot of exciton-cavity anticrossing as $V_{\mathrm{app}}$ is changed from $-0.05$ to $-0.40\mathrm{V}$, corresponding to detunings ranging from $\delta =+450\mu \mathrm{eV}$ to $\delta =-260\mu \mathrm{eV}$. The open circles correspond to experimental data while the solid lines are fits to the theory. Selected curves close to resonance ($\delta =0\mu \mathrm{eV}$) are presented in the bottom right panel showing the excellent agreement between the observed and calculated spectral functions. (Top right panel) Schematic of the layer structure of the device.

Figure 2

(a) Spectra of the exciton polaritons at resonance as a function of excitation power. The circles correspond to experimental data, while the solid lines are fits to the theory. In (b), the fitting parameters are displayed as they change with increasing excitation power density. Panel (c) shows the theoretically expected Rabi splitting at resonance (filled black squares) and the one obtained from the observed positions of the peaks in the PL spectra (open blue circles).

Figure 3

(a) Spectra of the exciton polaritons at resonance as a function of temperature. The circles correspond to experimental data, while the solid lines are fits to the theory. In (b), the fitting parameters are displayed as they change with increasing temperature. Panel (c) shows the theoretically expected Rabi splitting at resonance (filled black squares) and the one obtained from the observed positions of the peaks in the PL spectra (open blue circles).