On-chip single-photon sources are key components for integrated photonic quantum technologies. Semiconductor quantum dots can exhibit near-ideal single-photon emission, but this can be significantly degraded in on-chip geometries owing to nearby etched surfaces. A long-proposed solution to improve the indistinguishablility is to use the Purcell effect to reduce the radiative lifetime. However, until now only modest Purcell enhancements have been observed. Here we use pulsed resonant excitation to eliminate slow relaxation paths, revealing a highly Purcell-shortened radiative lifetime (22.7 ps) in a waveguide-coupled quantum dot-photonic crystal cavity system. This leads to near-lifetime-limited single-photon emission that retains high indistinguishablility (93.9%) on a timescale in which 20 photons may be emitted. Nearly background-free pulsed resonance fluorescence is achieved under π-pulse excitation, enabling demonstration of an on-chip, on-demand single-photon source with very high potential repetition rates.

We directly observe the electromagnetic radiation emitted by electrons coherently oscillating between the two wells of a semiconductor coupled-quantum- well structure. Using time-resolved coherent detection of the submillimeter-wave radiation from these spatial charge oscillations, we trace up to fourteen oscillations at 1.5 THz before phase relaxation destroys the coherence of the oscillating wave packet. In addition to the oscillatory electromagnetic signal, we also observe an instantaneous signal from electricfield-induced optical rectification in the semiconductor structure

No abstract

Coherent scattering of light by a single quantum emitter is a fundamental process at the heart of many proposed quantum technologies. Unlike atomic systems, solid-state emitters couple to their host lattice by phonons. Using a quantum dot in an optical nanocavity, we resolve these interactions in both time and frequency domains, going beyond the atomic picture to develop a comprehensive model of light scattering from solid-state emitters. We find that even in the presence of a cavity, phonon coupling leads to a sideband that is completely insensitive to excitation conditions, and to a non-monotonic relationship between laser detuning and coherent fraction, both major deviations from atom-like behaviour. arXiv:1904.05284v2 [quant-ph]We model a quantum dot (QD) as a two level system (TLS) with ground state |0 and a single exciton state |X , with splitting ω X ( = 1). The QD is driven by a continuous wave laser with a frequency ω L and Rabi coupling Ω. The QD couples to both a vibrational environment and a low-Q optical cavity, which is characterised by the Hamiltonian [41]:

Electron-sublevel-anticrossing effects have been studied in coupled quantum wells where the exciton binding energy is comparable to the minimum sublevel splitting. The anticrossing was induced by applying an electric field to align the first and second sublevels of adjacent wells. In this situation the electron-hole Coulomb interaction has a strong effect on the splittings measured by optical techniques, because the optical spectra typically measure exciton energies rather than single-particle energies. The most striking effect is that the minimum splitting of the excitons associated with each of the split electron levels does not occur at the same field as for the minimum splitting of the bare-electron levels. One unexpected but readily observable consequence is that when the same electron-sublevel splitting is measured using two different pairs of intrawell and interwell exciton transitions, the field for minimum exciton splitting can differ by up to -10% from one pair of transitions to the other. We have constructed a variational model of the coupled excitons that explains these effects in terms of Coulomb mixing of the delocalized electron states. We have measured the exciton splittings directly by photocurrent spectroscopy in three GaAs/Alo 3Gao 7As multiple-quantum-well structures. The samples were similar in design 0 except that the Al Ga& As barrier thickness varied from 15 to 35 A. By fitting our variational model to the experimental anticrossing data, we have been able to deduce the actual bare-electron level splittings rather than the exciton splittings. Within the experimental accuracy, we find that the minimum splitting decreased exponentially with increasing barrier thickness, as would be expected for simple quantum-mechanical tunneling.