S. Varoutsis

Single photon emission from site-controlled pyramidal quantum dots

We demonstrate that a single photoexcited InGaAs semiconductor quantum dot (QD) grown by organo-metallic chemical vapor deposition on prepatterned substrates emits one photon at a time, with no uncontrolled background photon emission, making it an excellent single photon emitter. Moreover, our fabrication technique offers complete site control and small inhomogeneous broadening of QD arrays, which is essential for the practical implementation of QDs in efficient solid-state single photon emitting devices.

Indistinguishable single photons from a single-quantum dot in a two-dimensional photonic crystal cavity

We report on the spontaneous emission of a single-quantum dot embedded in a two-dimensional photonic crystal cavity. The resonant coupling between the dot and the strongly localized optical mode significantly shortens the spontaneous emission lifetime, so that the coherence time of the emitted photons is dominated by radiative effects: The emitted photons are indistinguishable, with a mean wave-packet overlap as high as 72%.

Single photon emission from individual GaAs quantum dots

We report on photon correlation measurements on a single quantum dot formed at fluctuations of the interface of a GaAs/GaAlAs quantum well. We demonstrate that under pulsed nonresonant excitation, the quantum dot emits a single photon per pulse. This shows that after the photon emission, there is no refill of the quantum dot by the nearby two-dimensional reservoir of delocalized states. The possibility of delivering Fourier transform limited single photons makes this system a good candidate for exciton- and photon-based quantum information processing schemes.

Submicron-diameter semiconductor pillar microcavities with very high quality factors

Pillar microcavities are subject to two common fabrication artifacts: Bragg mirror corrugation and oxide deposit cladding. In this letter the authors investigate the impact of these features on the quality factor. A quasiperiodic variation of the quality factor as a function of the pillar diameter is experimentally observed and well described by theory. Moreover, observation of quality factors in excess of 1500, close to the theoretical limit, is reported for 600-nm-diameter GaAs micropillars bounded by AlGaAs∕GaAs Bragg mirrors.

Fast radiative quantum dots: From single to multiple photon emission

Photon correlation measurements are performed on single GaAs quantum dots with various excitonic radiative lifetimes. A continuous increase of the probability that the quantum dot emits more than one photon per excitation pulse is observed when decreasing the exciton radiative lifetime. The authors show that this increase is due to recapture processes into the quantum dot. A model for the second-order autocorrelation function including relaxation processes is developed and gives good description of the experimental observations.

Reactive-ion etching of high-Q and submicron-diameter GaAs∕AlAs micropillar cavities

We present a fabrication process allowing the realization of high-Q and small-diameter micropillar cavities. The fabrication involves molecular beam epitaxy, electron-beam lithography, and reactive ion etching (RIE). The introduction of O2 to the SiCl4 RIE plasma and the dynamic adjustment of its flow rate enable the control of the etched profile throughout the process, through the deposition of silicon oxide on the vertical etched surfaces. The resulting cavities have very smooth, straight, and vertical sidewalls and remain optically and mechanically stable for long periods of time. The optical modes sustained by these cavities exhibit record quality factors in excess of 1200 for pillar diameters close to 400nm, which underscores the quality of our process.

High-Q whispering-gallery modes in GaAs∕AlOx microdisks

We report on the fabrication of microdisks on an AlOx pedestal. We develop a process using electron beam lithography, a chemical etching, and selective oxidation. InAs self-assembled quantum dots are used as a broad band source to probe the optical modes of the microdisks. With this process, we observe whispering-gallery modes, with quality factors as large as 12 500 for 2-μm-diam microdisks.

Study of the Quality Factor of Micropillar Cavity

We study micropillar cavity and we show that their Q-factor can exhibit an oscillatory behavior. We provide an analysis of the physical mechanisms at the origin of these oscillations and a comparison with experimental measurements.

Indistinguishable single photons from a single quantum dot

This work reports on development of a source of indistinguishable photons based on a single quantum dot emitter coupled to a pillar microcavity.

Controlling coherence in single photon microcavity emitters

Physical considerations for the restoration of photon indistinguishability and entanglement in the emission of a quantum dot, the constraints on cavity design, and the technological issues associated with fabrication are discussed. Devices fabricated as solutions to these problems, and in particular microcavities capable of restoring photon indistinguishability are presented. Work towards cavities capable of restoring entanglement in the biexciton-exciton photon cascade is also discussed.