Note that the ordering of the states in the figure follows the occupancy, while the emission energies of the radiative excitonic complexes depend not only on the occupancy but also on confinement and correlation effects. Nonradiative processes (black arrows) are generally present and can for some transitions be dominant here only the nonradiative decays of the bright excitons are indicated explicitly. Furthermore, spin-flip processes (gray arrows) couple bright and dark excitons. The negative (positive) trion decays to a single electron (hole) by emission of circularly polarized light with the helicity depending on the additional carrier. The biexciton may decay to one of the two bright exciton states by emission of a horizontally ( H) or vertically ( V) polarized photon. The pseudospin states are discussed in the text.
MEETINONE REVIEW FULL
The full (empty) circles indicate the electron (hole) configuration in the conduction (valence) band s shells of the quantum dot. The lowest-energy confined states in quantum dots and the transitions between them. For Stranski-Krastanov quantum dots, an asymmetric confinement potential leads to a significant offset between the electron and hole. (e), (g), and (i) illustrate the wave functions along the growth axis z for the respective type of quantum dots. For interface-fluctuation quantum dots (f) the in-plane motion of electrons and holes may become correlated as shown by the purple exciton wave function and could lead to a giant oscillator strength. The electron (hole) wave function is shown as a shaded blue (red) oval. (d), (f), and (h) illustrate the confinement potentials, where dark, neutral, and bright gray indicate AlGaAs, GaAs, and InAs, respectively, for the three types of quantum dots shown above. (a)–(c) Atomic-force micrographs (AFMs) of uncapped quantum dots for (a) Stranski-Krastanov quantum dots of InAs, (b) interface fluctuations of GaAs, and (c) droplet epitaxy quantum dots of GaAs displaying the surface topography with bright (dark) colors indicating high (low) features. Finally, the progress and future prospects of applications in quantum-information processing are considered. The introduced concepts are generally applicable in quantum nanophotonics and apply to a large extent also to other quantum emitters, such as molecules, nitrogen vacancy centers, or atoms. This review summarizes the general theoretical framework of photon emission including the role of dephasing processes and applies it to photonic nanostructures of current interest, such as photonic-crystal cavities and waveguides, dielectric nanowires, and plasmonic waveguides. Furthermore, highly efficient single-photon sources and giant photon nonlinearities may be implemented with immediate applications for photonic quantum-information processing. The ability to engineer the light-matter interaction strength in integrated photonic nanostructures enables a range of fundamental quantum-electrodynamics experiments on, e.g., spontaneous-emission control, modified Lamb shifts, and enhanced dipole-dipole interaction. This manuscript reviews quantum optics with excitons in single quantum dots embedded in photonic nanostructures. In particular, the combination with semiconductor quantum dots has proven successful. Photonic nanostructures provide a means of tailoring the interaction between light and matter and the past decade has witnessed tremendous experimental and theoretical progress on this subject.
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