Frequency cavity pulling induced by a single semiconductor quantum dot

We investigate the emission properties of a single semiconductor quantum dot deterministically coupled to a confined optical mode in the weak-coupling regime. A strong spectral pulling, broadening, and narrowing of the cavity mode emission is evidenced when changing the spectral detuning between the emitter and the cavity. These features are theoretically accounted for by considering the phonon assisted emission of the quantum dot transition. These observations highlight a regime of cavity quantum electrodynamics scarcely investigated so far, involving spectrally broad emitters.

Figure 1

(a) System under investigation: a single QD is coupled to the confined optical mode of a micropillar cavity. The emission from the cavity channel is measured. We study two pillars: the first one embeds QD1 nondeterministically coupled to the mode, whereas the second one is deterministically and optimally coupled to QD2. Both pillars operate in the weak-coupling regime. (b) Emission spectra measured for various temperatures on QD1, presenting a poor coupling to the pillar mode. The two narrow emission lines correspond to the single QD emission lines and the broad emission to the cavity mode. The red and blue lines are Lorentzian fits to the experimental data. (c)–(e) Characteristics of the QD and cavity system deduced from emission spectroscopy: energy (c), intensity (d), and linewidth (e) of the QD (black) emission line and the cavity (red) emission line.

Figure 2

(a) Emission intensity as a function of energy and temperature for the pillar coupled to QD2. (b) and (c) Emission spectra extracted from the temperature flow presented in (a), corresponding to the two vertical white lines. Black symbols are the experimental points, black lines are the fits with the sum of three Lorentzian peaks, red line is a cavity peak, and blue lines are the CX and XX peaks. (d)–(f) Characteristics of the QD2-pillar device deduced by fitting the spectra with sums of Lorentzian peaks: energy (top), intensity (middle), and linewidth (bottom) of the QD (black) emission line and the cavity (red) emission lines. The QD linewidth, which is below the spectral resolution for all temperatures, is not shown. (g) Calculated energies of the apparent QD (black) and mode (red) lines as a function of temperature. The red dotted line is the bare cavity mode energy. (h) Calculated normalized emission intensity of the QD line (black) and the mode line (red) as a function of temperature. (i) Calculated width of the apparent cavity line as a function of temperature.

Figure 3

Cavity pulling induced by the QD phonon bath: (a) calculated emission spectra for a QD-cavity detuning of 1 meV at 40 K for a bare cavity of $Q=1000$. Green line is the calculated emission spectrum $S_{\mathrm{QD}}$ of the QD state coupled to the phonon bath. Red line is the cavity spectral function $S_{\mathrm{cav}}$. Black curve is the calculated emission spectrum $S$ of the coupled QD-cavity system. (b)–(d) Calculated emission characteristic for the cavity emission line as a function of detuning with the QD line for $T=20$ K. (b) Energy of the cavity line with respect to the QD energy. (c) Intensity of the cavity line. (d) Linewidth of the cavity line (logarithmic scale). Three bare cavity quality factors are considered: $Q=1000$ (black), 3000 (red), and 5000 (green). In (b), the case of $Q=5000$ is not shown for clarity and the black (respectively, blue) solid line is the bare QD (respectively, cavity) frequency. The dotted lines are the linear approximations of Eq. (1). In (d), the horizontal lines show the bare cavity linewidth. Lines in (c) are the normalized intensity of the cavity-filtered 1PL:$\int S_{\mathrm{cav}}\left(\omega \right){\Gamma }_{1\mathrm{PL}}(T,\omega )d\omega /\Gamma$.