Xudong Fan

Coupling semiconductor nanocrystals to a fused-silica microsphere: a quantum-dot microcavity with extremely high Q factors

We demonstrate a quantum-dot microcavity by coupling core-shell semiconductor nanocrystals to a fused-silica microsphere. We show that the composite microcavity can feature Q factors of the order of 10(8), providing a model system for investigating cavity QED and microlasers at the level of single quantum dots.

Pure dephasing induced by exciton–phonon interactions in narrow GaAs quantum wells

Abstract We investigate both dephasing and population relaxation of excitons localized in quantum dot like islands in narrow GaAs quantum wells by using stimulated photon echoes. A direct comparison of these two closely related decay processes reveals a pure dephasing contribution that dominates excitonic dephasing at elevated temperatures but does not involve exciton population relaxation. The pure dephasing contribution arises from coupling of excitonic states with a continuum of acoustic phonons and is enhanced by 3D quantum confinement. Both the magnitude and the temperature dependence of the pure dephasing rate can be described by a theoretical model that generalizes the Huang–Rhys theory of F-centers.

High-Q whispering gallery modes from a composite system of GaAs quantum well and fused silica microsphere

We demonstrate a composite system consisting of a GaAs quantum well structure placed in the evanescent field of a fused silica microsphere and show evanescent coupling between excitons in the quantum well and high-Q whispering gallery modes of the composite system. The composite system allows separate engineering of photonic and electronic confinement and can take advantage of high-Q factor and small mode volume of fused silica microspheres.

Microcavities combining a semiconductor with a fused-silica microsphere

We report studies of a novel microcavity system that combines a semiconductor quantum well with a fused-silica microsphere. We show that excitonic photoluminescence from the quantum well couples efficiently into whispering-gallery modes. Using a resonant light-scattering technique, we demonstrate that the Q factor of the combined system exceeds 10(5) . Our studies also point to the necessity of using semiconductor nanostructures with a capping layer no more than a few nanometers thick.

Attaching nanocrystals to a dielectric microsphere: a quantum dot microcavity with extremely high Q-factors

We have developed a novel quantum dot microcavity by attaching ZnS-capped CdSe nanocrystals to a fused silica microsphere. The composite microcavity system features extremely small mode volume and a Q-factor approaching 10/sup 7/. It allows us to separately engineer electronic and photonic confinement and opens up a new avenue for investigating laser emission and strong light-matter coupling at the mesoscopic level of a single QD and for realizing quantum logic gates based on cavity QED. We have investigated the mode structure of the composite microcavity system by putting the microspheres in contact with a high index prism to couple whispering gallery modes (WGM) out of the microsphere. A portion of photoluminescence spectrum of the WGMs is shown where the CdSe nanocrystals are excited above the band gap.

Pure dephasing induced by exciton-phonon interactions in GaAs quantum dots

We report studies of exciton dephasing in quantum dot (QD)-like islands in narrow GaAs quantum wells (QWs). Using three pulse transient four-wave mixing (FWM), we compare dephasing rates directly with population decay rates. This comparison reveals a pure dephasing process that dominates excitonic dephasing at elevated temperatures but does not involve exciton population relaxation.

Laser emission from semiconductor microcavities: transition from nonperturbative to perturbative regimes

We present experimental studies of laser emission in the nonperturbative regime in a GaAs quantum well (QW) microcavity. By tuning the cavity resonance to the low energy side of the inhomogeneous exciton distribution, we are able to achieve laser emission at exciton densities well below the exciton saturation density at which cavity polaritons vanish.

Biexcitonic effects in semiconductor microcavities

In this paper we present experimental and theoretical investigations of effects of biexcitons on coupled exciton-photon excitations, or cavity polaritons, in a GaAs quantum well (QW) microcavity. Using polarization-dependent transient pump-probe spectroscopy, we show that biexcitonic effects can result in a significant increase in normal mode splitting (NMS) of cavity polaritons, in sharp contrast to effects of band filling and exciton ionization that reduce the NMS. A theoretical model based on modified optical Bloch equations is developed to describe qualitatively effects of biexcitons in semiconductor microcavities.