A. Tahraoui

Nuclear spin switch in semiconductor quantum dots

We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with circularly polarized light, the nuclei of atoms constituting the dot can be driven into a bistable regime, in which either a thresholdlike enhancement or reduction of the local nuclear field by up to 3 T can be generated by varying the pumping intensity. The excitation power threshold for such a nuclear spin switch is found to depend on both the external magnetic and electric fields. The switch is shown to arise from the strong feedback of the nuclear spin polarization on the dynamics of the spin transfer from electrons to the nuclei of the dot.

Whispering gallery resonances in semiconductor micropillars

In this letter, the authors observe high quality (Q up to 20u2009000) whispering gallery modes (WGMs) with small modal volumes V∼0.3μm3 in 4–5μm Al(Ga)As∕GaAs micropillars by employing an experimental geometry in which both excitation and collection of emission are in a direction normal to the sidewalls of the pillars. They show that WGMs provide at least two times larger values of the figure of merit for strong coupling applications Q∕V compared to “photonic dot” states in pillars with comparable size.

Control of polarized single quantum dot emission in high-quality-factor microcavity pillars

Small size microcavity pillars with elliptical cross section and high quality factors Q are reported and are shown to provide nearly 100% linearly polarized single photon sources. It is shown that the polarization of the emission of quantum dots embedded within the pillars can be controlled by using the coupling of the dot emission with the photonic modes. A notable dependence of the Q value is found on the polarization of the mode even though calculations of the mode profiles show that the electric field distribution is very similar.

High Q modes in elliptical microcavity pillars

The degenerate fundamental mode of a microcavity pillar structure with circular cross section splits into two linearly polarized modes when the shape is changed to elliptical. The quality factor Q of these modes is very different. This letter demonstrates that the high Q mode provides better values of the figure of merit for strong coupling applications, Q∕V), where V is the modal volume, compared to values obtainable in circular structures. The difference in Q is shown to be a consequence of the polarization dependence of the losses through the microcavity mirrors.

SINGLE PHOTON SOURCES BASED UPON SINGLE QUANTUM DOTS IN SEMICONDUCTOR MICROCAVITY PILLARS

Semiconductor microcavity pillars with both circular and elliptical cross-section containing semiconductor quantum dots are shown to be good candidates for efficient single photon sources. Pillars with small diameters are shown to have exceptionally high quality factors and the reduction in the measured quality factor as the pillar diameter is reduced is shown to agree well with finite difference time domain simulation. These pillars exhibit a Purcell enhancement of the quantum dot emission when the dots are on-resonance with the cavity mode and strong photon antibunching. The use of the polarized modes of an elliptical micropillar allows the polarization of the emitted single photons to be selected.

Splitting and lasing of whispering gallery modes in quantum dot micropillars

Whispering gallery mode splitting in high quality-factor InAs quantum dot micropillars is observed and attributed to resonant scattering from the dots themselves. Low-threshold multimode lasing with beta-factors approaching unity is demonstrated.

Control of polarization and mode mapping of small volume high Q micropillars

We show that the polarization of the emission of a single quantum dot embedded within a microcavity pillar of elliptical cross section can be completely controlled and even switched between two orthogonal linear polarizations by changing the coupling of the dot emission with the polarized photonic modes. We also measure the spatial profile of the emission of a series of pillars with different ellipticities and show that the results can be well described by simple theoretical modeling of the modes of an infinite length elliptical cylinder.

Modes of the L3 defect cavity in InAs quantum dot photonic crystals

We investigate the longest wavelength modes of an L3 photonic crystal cavity. Reordering of modes due to hole displacement is shown theoretically and experimentally. Cavity optimization is explained in terms of dipolar emission cancellation.

Coherent control of single quantum dot exciton embedded in a photodiode

We study the coherent properties of a two-level system based on the ground state neutral exciton of a single InGaAs self-assembled quantum dot (SAQD) embedded in an n-i-Schottky diode. By using a photocurrent technique, we observe Rabi oscillations of the exciton population for pulse-areas of up to 6π. We perform two pulse quantum interference experiments to deduce the decoherence rate.