We show that resonance fluorescence, i.e., the resonant emission of a coherently driven two-level system, can be realized with a semiconductor quantum dot. The dot is embedded in a planar optical microcavity and excited in a waveguide mode so as to discriminate its emission from residual laser scattering. The transition from the weak to the strong excitation regime is characterized by the emergence of oscillations in the first-order correlation function of the fluorescence, $g(\tau )$, as measured by interferometry. The measurements correspond to a Mollow triplet with a Rabi splitting of up to $13.3\mu \mathrm{eV}$. Second-order correlation measurements further confirm nonclassical light emission.

Using photoluminescence spectroscopy, we have investigated the nature of Rabi oscillation damping during optical manipulation of excitonic qubits in self-assembled quantum dots. Rabi oscillations were recorded by varying the pulse amplitude for fixed pulse durations between $4\mathrm{ps}$ and $10\mathrm{ps}$. Up to five periods are visible, making it possible to quantify the excitation dependent damping. We find that this damping is more pronounced for shorter pulse widths and show that its origin is the nonresonant excitation of carriers in the wetting layer, most likely involving bound-to-continuum and continuum-to-bound transitions.

In a semiconductor quantum dot, the ${\Pi }_x$ and ${\Pi }_y$ transitions to the polarization eigenstates, $|x⟩$ and $|y⟩$, naturally form a three-level V-type system. Using low-temperature polarized photoluminescence spectroscopy, we have investigated the exciton dynamics arising under strong laser excitation. We also explicitly solved the density matrix equations for comparison with the experimental data. The polarization of the exciting field controls the coupling between the otherwise orthogonal states. In particular, when the system is initialized into $|y⟩$, a polarization-tailored pulse can swap the population into $|x⟩$, and vice versa, effectively operating on the exciton spin.

By investigating the polarization-dependent Rabi oscillations using photoluminescence spectroscopy, we determined the respective transition dipole moments of the two excited excitonic states ${\mathrm{|E}}_x〉$ and ${\mathrm{|E}}_y〉$ of a single self-assembled quantum dot that are nondegenerate due to shape anisotropy. We find that the ratio of the two dipole moments is close to the physical elongation ratio of the quantum dot.

Whispering gallery mode (WGM) optical microresonators have been shown to be the basis for sensors able to detect minute changes in their environment. This has made them a well-established platform for highly sensitive physical, chemical, and biological sensors. Microbottle resonators (MBR) are a type of WGM optical microresonator. They share characteristics with other, more established, resonator geometries such as cylinders and spheres, while presenting their unique spectral signature and other distinguishing features. In this review, we discuss recent advances in the theory and fabrication of different kinds of MBRs, including hollow ones, and their application to optofluidic sensing.