Dephasing of Triplet-Sideband Optical Emission of a Resonantly Driven $\mathrm{InAs}/\mathrm{GaAs}$ Quantum Dot inside a Microcavity

Detailed properties of resonance fluorescence from a single quantum dot in a micropillar cavity are investigated, with particular focus on emission coherence in the dependence on optical driving field power and detuning. A power-dependent series over a wide range reveals characteristic Mollow triplet spectra with large Rabi splittings of $|\Omega |\le 15\mathrm{GHz}$. In particular, the effect of dephasing in terms of systematic spectral broadening $\propto {\Omega }^2$ of the Mollow sidebands is observed as a strong fingerprint of excitation-induced dephasing. Our results are in excellent agreement with predictions of a recently presented model on phonon-dressed quantum dot Mollow triplet emission in the cavity-QED regime.

Figure 1

(a) Single-QD neutral exciton ($X^0$) emission spectrally close to the fundamental mode (FM) of a $1.75\mu \mathrm{m}$ micropillar cavity, observed at quasiresonant $p$-shell excitation ($P_0\approx 50\mu \mathrm{W}$; $\Delta E(T)$: temperature-dependent QD-mode detuning). Inset: Time-resolved $X^0$ emission. (b) Schematic geometry of orthogonal excitation and detection.

Figure 2

(a) Power-dependent high-resolution spectra of $X^0$ emission at resonant ($\Delta =0$) cw excitation. (b) Mollow sideband splitting $|\Omega |\sim P_0^{1/2}$ extracted from (a). (c) Power-dependent Mollow sideband FWHM $\Delta \nu$ and total dephasing rate $\Gamma \propto {\Omega }^2$ from theoretical analysis of data in (a), indicative of excitation-induced dephasing (EID).

Figure 3

(a) HRPL of QD resonance fluorescence under excitation detuning $\Delta$ (see arrows) relative to the QD $s$ shell, taken at a fixed power of $P_0=16\mu \mathrm{W}$. Red (medium gray) traces: Lorentzian FWHM fits. (b) Spectral evolution of Mollow sidebands (red [medium gray]) with laser detuning $\Delta$ (black center trace), derived from (a). (c) Total sideband splitting in plot (b), together with a theory fit to evaluate the bare Rabi frequency $\Omega$. (d) Sideband FWHM vs laser detuning $\Delta$ from plot (a), revealing the phenomenon of FWHM reduction with increasing $\Delta$. Please note a reduced QD-FM detuning $\Delta E=+230\mu \mathrm{eV}$, yielding $T_1\sim 410\pm 20\mathrm{ps}$ and correspondingly larger FWHM by a factor of $\sim 1.6$ for $\Delta =0$ conditions with respect to Fig. 2c.