We use a laser-driven single (In, Ga) As quantum dot (QD) in the dressed-state regime of resonance fluorescence (T = 4 K) to observe the four D-1-transition lines of alkali atomic cesium (Cs) vapor at room temperature. We tune the frequency of the dressing continuous-wave laser in the vicinity of the bare QD resonance similar to 335.116 THz (similar to 894.592 nm) at constant excitation power and thereby controllably tune the center and side channel frequencies of the probe light, i.e., the Mollow triplet. Resonances between individual QD Mollow triplet lines and the atomic hyperfine-split transitions are clearly identified in the Cs absorption spectrum. Our results show that narrow-band (In, Ga) As QD resonance fluorescence (RF) is suitable to optically address individual transitions of the D-1 quadruplet without applying magnetic field or electric field tuning.

Applying high-power continuous-wave resonant s-shell excitation to a single self-assembled InGaAs quantum dot, we demonstrate the generation of postselected single-indistinguishable photons from the Mollow triplet sidebands. A sophisticated spatial filtering technique based on a double Michelson interferometer enabled us to separate the spectrally close lying individual Mollow components and perform almost background-free two-photon interference measurements. Showing high consistency with the results of an independent determination of the emission coherence of similar to 250 +/- 30 ps, our analysis reveals a close to ideal visibility contrast of up to 97%. Due to their easy spectral tunability and their distinct advantage of cascaded-photon emission between the individual Mollow sidebands, they resemble a versatile tool for quantum information applications.

We present both experimental and theoretical investigations of a laser-driven quantum dot (QD) in the dressed-state regime of resonance fluorescence. We explore the role of phonon scattering and pure dephasing on the detuning-dependence of the Mollow triplet and show that the triplet sidebands may spectrally broaden or narrow with increasing detuning. Based on a polaron master equation approach, which includes electron-phonon interaction nonperturbatively, we derive a fully analytical expression for the spectrum. With respect to detuning dependence, we identify a crossover between the regimes of spectral sideband narrowing or broadening. We also predict regimes of phonon-induced squeezing and anti-squeezing of the spectral resonances. A comparison of the theoretical predictions to detailed experimental studies on the laser detuning-dependence of Mollow triplet resonance emission from single In(Ga)As QDs reveals excellent agreement.

Semiconductor quantum dots (QDs) belong to the class of structures called “artificial” atoms which exhibit distinct quantum character. Self assembled quantum dot (SAQD) structures with high optical efficiency and relatively stable emission energies as compared to colloidal dot system make them ideal for quantum light generation. Such a single structure can also be suitably selected as a solid state-based platform to mimic quantum optical phenomena involving light matter interaction. Indeed a lot of theoretical and experimental studies in the past decade have focused on the above-mentioned aspects of SAQDs.

Charge-neutral excitons in semiconductor quantum dots (QDs) have a small finite energy separation caused by the anisotropic exchange splitting. Coherent excitation of neutral excitons will generally excite both exciton components, unless the excitation is parallel to one of the dipole axes. We present a polaron master equation model to describe two-exciton pumping using a coherent continuous wave pump field in the presence of a realistic anisotropic exchange splitting. We predict a five-peak incoherent spectrum, namely a Mollow quintuplet under general excitation conditions. We experimentally confirm such spectral quintuplets for In(Ga)As QDs and obtain very good agreement with theory.

Emission from a resonantly excited quantum emitter is a fascinating research topic within the field of quantum optics and is a useful source for different types of quantum light fields. The resonance spectrum consists of a single spectral line that develops into a triplet above saturation of the quantum emitter1,2,3. The three closely spaced photon channels from the resonance fluorescence have different photon statistical signatures4. We present a detailed photon statistics analysis of the resonance fluorescence emission triplet from a solid-state-based artificial atom, that is, a semiconductor quantum dot. The photon correlation measurements demonstrate both ‘single’ and ‘cascaded’ photon emission from the Mollow triplet sidebands5. The bright and narrow sideband emission (5.9 × 106 photons per second into the first lens) can be conveniently frequency-tuned by laser detuning over 15 times its linewidth (Δv ≈ 1.0 GHz). These unique properties make the Mollow triplet sideband emission a valuable light source for quantum light spectroscopy and quantum information applications, for example. Researchers demonstrate that an individual Mollow sideband channel of the resonance fluorescence from an InGaAs quantum dot can act as an efficient single-photon source. The central frequency of the bright and narrow sideband emission can be changed by laser detuning over a range spanning 15 times the emission linewidth.

We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally detuned continuous-wave laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20$%$ with respect to strictly resonant excitation can be achieved at $T=9$ K. Laser-frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the steady-state exciton density (which is proportional to the photoluminescence) is introduced which predicts a broadband incoherent coupling process mediated by electron-phonon scattering. Moreover, we investigate the coherence properties of the emitted light with respect to strictly resonant versus phonon-assisted excitation, revealing the importance of narrow band triggered emitter-state initialization for possible applications of a quantum dot exciton system as a qubit.

We report on the robustness of a detuned mode channel for reading out the relevant $s$-shell properties of a resonantly excited coupled quantum dot (QD) in a pillar microcavity. The line broadening of the QD $s$-shell is ``monitored'' by the mode signal with high conformity to the directly measured QD linewidth. The mode signal also monitors the saturation behavior of a near Fourier transform-limited photon emission from a resonantly excited QD. We also investigate the temperature dependence of the coupling mechanism between an off-resonant QD and a cavity mode under pure resonant excitation of the quantum emitter.

The emission characteristics of a system of one quantum dot (QD) nonresonantly coupled to two distinct detuned modes of a surrounding microcavity have been investigated, revealing strong interconnection in terms of photon anti-correlation in QD-mode and mode-mode cross correlations. Temperature-dependent lifetime measurements demonstrate that the QD emission dynamics is transferred to the mode channels through the process of nonresonant coupling, whereas the short coherence time of mode emission stays unperturbed by the QD-mode detuning. Power-dependent studies under pure-resonant QD excitation have traced the strong emitter-mode coupling to both an excited and the fundamental micropillar mode with spectral detunings of up to 3.7 meV.