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We review recent studies of cavity switching induced by the optical injection of free carriers in micropillar cavities containing quantum dots. Using the quantum dots as a broadband internal light source and a streak camera as detector, we track the resonance frequencies for a large set of modes with picosecond time resolution. We report a record-fast switch-on time constant (1.5 ps) and observe major transient modifications of the modal structure of the micropillar on the 10 ps time scale: mode crossings are induced by a focused symmetric injection of free carriers, while a lifting of several mode degeneracies is observed when off-axis injection breaks the rotational symmetry of the micropillar. We show theoretically and experimentally that cavity switching can be used to tailor the dynamic properties of the coupled QD–cavity system. We report the generation of ultrashort spontaneous emission pulses (as short as 6 ps duration) by a collection of frequency-selected QDs in a switched pillar microcavity. These pulses display a very small coherence length, attractive for ultrafast speckle-free imaging. Moreover, the control of QD-mode coupling on the 10 ps time scale establishes cavity switching as an appealing resource for quantum photonics.

Silicon photonics based on CMOS technology is a very attractive platform to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of quantum key distribution protocols. We show record low propagation losses below 0.5 dB/cm and below 0.05 dB/cm for silicon and silicon nitride waveguides respectively. We will present our results on integrated components such as hybrid III-V on silicon lasers for weak coherent pulse generation, high-quality microresonators for entangled photon pair generation and we will show our recent developments on high crystalline quality NbN thin films with improved critical temperature for waveguide-integrated superconducting single photon detectors.

We experimentally demonstrate phase encoding in SHG with transparent all-dielectric metasurfaces. While a similar task was previously achieved with plasmonic metasurfaces for THG beam shaping, here we obtain three-order-of-magnitude higher generation efficiency without thermal dissipation.

We report the detection of individual emitters in silicon belonging to seven different families of optically active point defects. These fluorescent centers are created by carbon implantation of a commercial silicon- on-insulator wafer usually employed for integrated photonics. Single photon emission is demonstrated over the 1.1–1.55 μm range, spanning the O and C telecom bands. We analyze their photoluminescence spectra, dipolar emissions, and optical relaxation dynamics at 10 K. For a specific family, we show a constant emission intensity at saturation from 10 K to temperatures well above the 77 K liquid nitrogen temperature. Given the advanced control over nanofabrication and integration in silicon, these individual artificial atoms are promising systems to investigate for Si-based quantum technologies.

We report on a simple nanopost single-photon source geometry based on a quantum dot in a mesa placed on a metal mirror. A remarkably large Purcell enhancement of 9 for the smallest structure is obtained.

We report on ultrafast all-optical switching experiments performed on pillar microcavities containing a collection of quantum dots (QDs). Using QDs as a broadband internal light source and a detection setup based on a streak camera, we track in parallel the frequencies of a large set (>10) of resonant modes of an isolated micropillar during the entire duration of switching events and with a 2 ps temporal resolution. Being much faster and more convenient than standard approaches based on pump–probe spectroscopy, this method is very well suited forin-depth studies of cavity switching, noticeably in view of applications in the field of quantum photonics. We report as a first demonstrative example an investigation of the switch-on time constant tau_on dependence as a function of the pump power and the observation of a remarkably low value of tau-on(≈1.5 ps) for optimized pumping conditions. As a second illustration, we report the observation of a transient lifting of the degeneracy of a polarization-degenerate cavity mode, induced by a non-centrosymmetric injection of free carriers.

Tapered nanowire antennas have emerged as a versatile solid-state platform for quantum optics. These broadband photonic structures efficiently funnel the spontaneous emission of an embedded quantum dot into a directive free-space beam. They find application in the realization of bright sources of quantum light, and enable the implementation of giant optical non-linearities, at the single-photon level. In this work, we discuss advances aiming at further optimizing this light-matter interface. In particular, recent measurements revealed that the thermal excitation of a single nanowire vibration mode can have a sizeable influence on the quantum dot optical linewidth. This motivated a comprehensive theoretical analysis, which shows that the thermally-driven vibrations of the nanowire have a major impact on the quantum dot light emission spectrum. Even at liquid helium temperatures, these prevent the emission of indistinguishable photons. To overcome this intrinsic limitation, we propose several designs that restore photon indistinguishability thanks to a specific engineering of the mechanical properties of the nanowire. We anticipate that such a mechanical optimization will also play a key role in the development of other high-performance light-matter interfaces based on nanostructures.

We demonstrate an AlGaAs metasurface that implements second harmonic generation with engineered phase-front. Nonlinear holography is obtained, with three-order-of-magnitude higher conversion efficiency than in χ(3) plasmonic metasurfaces.

International audience; To deliver an optimal performance for photonic quantum technologies, semiconductor quantum dots should be integrated in a carefully designed photonic structure. Here, we introduce a nanowire optical nanocavity designed for free-space emission. Thanks to its ultrasmall mode volume, this simple structure offers a large acceleration of spontaneous emission (predicted Purcell factor of 6.3) that is maintained over a 30-nm bandwidth. In addition, a dielectric screening effect strongly suppresses the emission into the 3D continuum of radiation modes. The fraction of spontaneous emission funneled into the cavity mode reaches 0.98 at resonance and exceeds 0.95 over a 100-nm spectral range. Close-to-optimal collection efficiency is maintained over an equivalent bandwidth and reaches a predicted value of 0.54 at resonance for a first lens with a numerical aperture (NA) of 0.75. As a first experimental demonstration of this concept, we fabricate an Au–SiO2–GaAs device embedding isolated InAs quantum dots. We measure a maximal acceleration of spontaneous emission by a factor as large as 5.6 and a bright quantum dot emission (collection efficiency of 0.35 into NA¼0.75). This nanowire cavity constitutes a promising building block to realize advanced sources of quantum light for a broad range of material systems.

International audience; We use strain to statically tune the semiconductor band gap of individual InAs quantum dots (QDs) embedded in a GaAs photonic wire featuring very efficient single photon collection efficiency. Thanks to the geometry of the structure, we are able to shift the QD excitonic transition by more than 20 meV by using nano-manipulators to apply the stress. Moreover, owing to the strong transverse strain gradient generated in the structure, we can relatively tune two QDs located in the wire waveguide and bring them in resonance, opening the way to the observation of collective effects such as superradiance.

International audience; In the field of quantum technologies, the superconducting nanowire single photon detector(SNSPD) is nowadays well recognized as a key enabling device. SNSPDs combine high detectionefficiency in the visible and near IR spectral ranges, timing jitter as low as 10 ps, low dark count rate(90% [1]) andpolarization-insensitive [2,3] detection efficiency. We consider designs based on the integration of thenanowire within an optical microcavity (compatible with the plug-and-play configuration) or on topof an optical waveguide (preferred approach for integration in photonic circuits). I will finally discussnovel application prospects of such detectors, with emphasis on photon-number resolution.

International audience; Summary form only given. Optical logic down to the single photon level holds the promise of data processing with a better energy efficiency than electronic devices [1]. In addition, preservation of quantum coherence in such logical components would enable optical quantum logical gates [2-8]. Optical logic requires optical non-linearities to allow for photon-photon interactions. Non-linearities usually appear for large intensities, but discrete transitions in a well coupled single two-level system allow for giant non-linearities operating at the single photon level.This is achieved by engineering what has been coined a "one-dimensional atom" [2], wherein a light emitter is predominantly coupled to a single propagating spatial mode. This favored coupling with a traveling mode is obtained either in a resonant optical cavity [3,4] or with non-resonant field confinement such as in single mode waveguides [5,6] or through the interaction with a focused optical beam [7,8] . Here we take advantage of the large coupling efficiency and the broadband operation of a photonic wire containing a semiconductor quantum dot (QD) [9] to implement a transistor using two different optical QD transitions. Our system is made of a single InAs QD embedded in a GaAs tapered photonic wire (fig. 1a). This system, in which the QD is efficiently coupled to a single guided mode, has been exploited to realize ultrabright single-photon sources [9]. We exploit here its broad operation bandwidth (>100 nm around 950 nm) to efficiently address two different transitions of the QD with two different laser beams to implement a two-color giant non-linearity: a weak probe laser has its reflectivity controlled by a few photons of the control laser.

Optical nonlinearities usually appear for large intensities, but discrete transitions allow for giant nonlinearities operating at the single-photon level. This has been demonstrated in the last decade for a single optical mode with cold atomic gases, or single two-level systems coupled to light via a tailored photonic environment. Here, we demonstrate a two-mode giant nonlinearity with a single semiconductor quantum dot (QD) embedded in a photonic wire antenna. We exploit two detuned optical transitions associated with the exciton-biexciton QD level scheme. Owing to the broadband waveguide antenna, the two transitions are efficiently interfaced with two free-space laser beams. The reflection of one laser beam is then controlled by the other beam, with a threshold power as low as 10 photons per exciton lifetime (1.6 nW). Such a two-color nonlinearity opens appealing perspectives for the ealization of ultralow-power logical gates and optical quantum gates, and could also be implemented in an integrated photonic circuit based on planar waveguides.

We present the modeling of an active nonlinear source designed for spontaneous parametric down-conversion in an AlGaAs waveguide. Electrically pumped InAs Quantum Dots embedded in the waveguide core provide the gain necessary for the lasing of a second-order pump mode at about 980 nm, which in turns generates two cross-polarized fundamental signal and idler modes with wavelengths around 1960 nm. We numerically evaluate the source efficiency and highlight the advantages provided by our choice of active medium for the fabrication of the device.

International audience; We propose a novel “hourglass”-shaped design for highly efficient generation and collection of quantum light. The design features a quantum dot in a photonic nanowire sandwiched between tapered Bragg reflectors. For a Purcell factor of 9, the design features a spontaneous emission coupling of0.993 to the cavity mode enabled by the strong dielectric screening of radiation modes. Thanks to a highly reflecting bottom mirror, we furthermore demonstrate a collection efficiency of 0.95 to a Gaussian profile. Finally, this photonic structure features a broad operation bandwidth, as large as 11 nm.

A quantum dot embedded in a trumpet nanowire has been shown to be a good candidate for realising an efficient on-demand single-photon source [1, 2]. At the lateral quantum dot position the diameter of the nanowire only supports two guided modes — the HE11 and TE01 modes. These modes are excited by the quantum dot after recombination of an electron-hole pair. The slow expansion of the nanowire diameter secures an adiabatic propagation of the modes through the taper meaning that the occupation of the HE11 and TE01 modes will remain the same at the top of the trumpet nanowire (see Fig. 1 right). It is for now not possible to control the radial position of the quantum dot in the nanowires and thus it is important to experimentally determine this after fabrication.

International audience; The performance of superconducting-nanowire single-photon detectors depends on the efficiency of light absorption in the ultrathin (3-8 nm) superconducting nanowire. In this work, we will discuss two approaches to boost light absorption: coupling the nanowire to the evanescent field propagating in a waveguide and enclosing the nanowire in an optical cavity. The latter method is the most widely used, but it is intrinsically very sensitive to the polarization of light. To overcome this issue, we propose some innovative cavity designs which make use of high-index (n >2) dielectrics. With this technique, highly-efficient polarization-insensitive devices can be easily implemented.

International audience; In this paper, the design of superconducting-nanowire single-photon detectors which are insensitive to the polarization of the incident light is investigated. By using high-refractive-index dielectrics, the index mismatch between the nanowire and the surrounding media is reduced. This enhances the absorption of light with electric field vector perpendicular to the nanowire segments, which is generally hindered in these kind of detectors. Building on this principle and focusing on NbTiN nanowire devices, we present several easy-to-realize cavity architectures which allow high absorption efficiency (in excess of 90%) and polarization insensitivity simultaneously. Designs based on ultranarrow nanowires, for which the polarization sensitivity is much more marked, are also presented. Finally, we briefly discuss the specific advantages of this approach in the case of WSi or MoSi nanowires.

We perform coherent non-linear spectroscopy of individual excitons strongly confined in single InAs quantum dots (QDs). The retrieval of their intrinsically weak four-wave mixing (FWM) response is enabled by a one-dimensional dielectric waveguide antenna. Compared to a similar QD embedded in bulk media, the FWM detection sensitivity is enhanced by up to four orders of magnitude, over a broad operation bandwidth. Three-beam FWM is employed to investigate coherence and population dynamics within individual QD transitions. We retrieve their homogenous dephasing in a presence of spectral wandering. Two-dimensional FWM reveals off-resonant F\"orster coupling between a pair of distinct QDs embedded in the antenna. We also detect a higher order QD non-linearity (six-wave mixing) and use it to coherently control the FWM transient. Waveguide antennas enable to conceive multi-color coherent manipulation schemes of individual emitters., Comment: 7 pages, 8 Figures

Micropillar cavities are potential candidates for high-efficiency single-photon sources and are testbeds for cavity quantum electrodynamics experiments. In both applications a high quality (Q) factor is desired. It was recently shown that the Q of high-Q semiconductor micropillar cavities exhibit pronounced quasi-periodic variations in the regime from 1 to 4 μm, and a detailed understanding of the variational behavior of the Q is required. Here, we study the origin of these variations using a multi-mode Fabry-Perot model appropriate for this regime. We analyze in detail contributions to the effective reflectivity of the fundamental mode arising from coupling to scattering channels involving higher-order cavity modes and propagating Bloch modes in the distributed Bragg reflectors (DBRs). We show how these weak contributions lead to strong variations of the Q factor, and we relate the average periodicity of these variations to the thickness of the DBRs and the derivative of the effective indices of the guided Bloch modes. We also examine the influence of various geometrical parameters, including the number of DBR layers pairs, the amplitude of the corrugation of the pillar sidewalls and the number of etched layer pairs in the bottom DBR on the Q versus diameter relation. Comparisons are made between extensive numerical simulations and experimental measurements, and a good qualitative agreement is found.

We present cavity quantum electrodynamics (cQED) effects in electrically driven high quality (high-Q) quantum dot-micropillar cavities. An optimized current injection scheme is employed, which enables simultaneously efficient electrical pumping and efficient out-coupling of light: A ring-shaped electrical contact leaving the upper facet of the pillars free from any absorbing material is used for efficient current injection and additionally serves as an aperture. This approach helps to suppress the detection of spontaneous emission from QDs through the sidewalls of the micropillars and leads to very clean electroluminescence spectra. Temperature tuning of single quantum dots (QDs) excitons allows us to observe Purcell-enhancement of the spontaneous emission for QDs interaction with the fundamental mode as well as higher order modes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present the experimental realization of a quantum fiber-pigtail. The device consists of a semiconductor quantum-dot embedded into a conical photonic wire that is directly connected to the core of a fiber-pigtail. We demonstrate a photon collection efficiency at the output of the fiber of 5.8% and suggest realistic improvements for the implementation of a useful device in the context of quantum information. We also discuss potential applications in scanning probe microscopy. The approach is generic and transferable to other materials including diamond and silicon.

International audience; We introduce a calibration method to quantify the impact of external mechanical stress on the emission wavelength of distinct quantum dots (QDs). Specifically, these emitters are integrated in a cross-section of a semiconductor core wire and experience a longitudinal strain that is induced by an amorphous capping shell. Detailed numerical simulations show that, thanks to the shell mechanical isotropy, the strain in the core is uniform, which enables a direct comparison of the QD responses. Moreover, the core strain is determined in situ by an optical measurement, yielding reliable values for the QD emission tuning slope. This calibration technique is applied to self-assembled InAs QDs submitted to incremental elongation along their growth axis. In contrast to recent studies conducted on similar QDs submitted to a uniaxial stress perpendicular to the growth direction, optical spectroscopy reveals up to ten times larger tuning slopes, with a moderate dispersion. These results highlight the importance of the stress direction to optimize the QD optical shift, with general implications, both in static and dynamic regimes. As such, they are in particular relevant for the development of wavelength-tunable single-photon sources or hybrid QD opto-mechanical systems.

We report the observation of high- Q whispering gallery modes ( Q > 10 000) in GaAs/AlAs pillar microcavities containing InAs quantum dots as an internal probe. A simple model based on the effective index method describes precisely the evolution of the free spectral range with the pillar diameter.

We present a novel single-mode single photon source exploiting the emission of a semiconductor quantum dot (QD) located inside a photonic wire. We first show theoretically that for optimized designs, more than 95% of the QD spontaneous emission (SE) can be injected into the fundamental guided mode of the photonic wire. A single photon collection efficiency of 17% is measured in a preliminary experiment performed on a single InAs QD located within a 250 nm diameter cylinder of GaAs. Because this photon collection strategy does not exploit the Purcell effect, it could also be efficiently applied to broadband single photon emitters such as F-centers in diamond.

We have switched GaAs/AlAs and AlGaAs/AlAs planar microcavities that operate in the “Original” (O) telecom band by exploiting the instantaneous electronic Kerr effect. We observe that the resonance frequency reversibly shifts within one picosecond when the nanostructure is pumped with low-energy photons. We investigate experimentally and theoretically the role of several parameters: the material backbone and its electronic bandgap, the quality factor, and the duration of the switch pulse. The magnitude of the frequency shift is reduced when the backbone of the central λ-layer has a greater electronic bandgap compared to the cavity resonance frequency and the frequency of the pump. This observation is caused by the fact that pumping with photon energies near the bandgap resonantly enhances the switched magnitude. We thus find that cavities operating in the telecom O-band are more amenable to ultrafast Kerr switching than those operating at lower frequencies, such as the C-band. Our results indicate that the large bandgap of AlGaAs/AlAs cavity allows to tune both the pump and the probe to the telecom range to perform Kerr switching without detrimental two-photon absorption. We observe that the magnitude of the resonance frequency shift decreases with increasing quality factor of the cavity. Our model shows that the magnitude of the resonance frequency shift depends on the pump pulse duration and is maximized when the duration matches the cavity storage time to within a factor two. In our experiments, we obtain a maximum shift of the cavity resonance relative to the cavity linewidth of 20%. We project that the shift of the cavity resonance can be increased twofold with a pump pulse duration that better matches the cavity storage time. We provide the essential parameter settings for different materials so that the frequency shift of the cavity resonance can be maximized using the electronic Kerr effect.

SPIE optics + optoelectronics. Prague, Czech Republic, 13-16 April 2015; International audience; The ability to control the temporal shape of single-photon pulses is highly desirable in quantum information processing. For instance, it has been shown that Gaussian pulses are best suited for linear optics quantum computing1. By mimicking the time-reversal of a spontaneous emission event, it also allows to optimize the absorption of the prepared photons by a quantum emitter. In this work we investigate the potential of using fast modifications of the detuning between an atomic system and a cavity mode during photon emission to reach this goal. We compare two approaches consisting of varying the emitter or cavity frequency. The latter, achievable by a fast modification of the refractive index of a solid state cavity, will be shown to have negligible influence on the photon spectrum. It allows to create Gaussian pulses interacting with a fidelity to the target photons of 99%, as well as time-reversed photons absorbed by an atom in a cavity with a probability of 93%.

To demonstrate strong coupling regime for a single quantum dot inside an optical microcavity, large oscillator strength quantum dots are needed. We show that quantum dots formed by the interface fluctuations of a thin GaAs quantum well are ideal systems for this purpose since they can present an oscillator strength larger than 100. By inserting a GaAs QD inside a state of the art microdisk microcavity, we demonstrate the strong coupling regime with a Rabi splitting of 400 μeV.

The Purcell effect leads to an enhancement of the spontaneous emission in a given cavity mode for an emitter located in a small volume cavity. This effect is well explained as a consequence of Fermi's golden rule in a particular photonic environment. In this paper we show an enhancement by a factor of up to 3.4 of the spontaneous emission of CdSe/ZnSe quantum dots located in a pillar microcavity. The sample consists of a λ/2-Znse cavity sandwiched between SiO 2 /TiO 2 Bragg mirrors and is etched to provide lateral optical confinement. The present study is based on a comparison between time-resolved photoluminescence measurements for dots inserted in a pillar cavity or in a bulk ZnSe layer. The photoluminescence decay shortening is quantitatively interpreted by calculating the theoretical maximum Purcell factor expected for different cavity modes in resonance with quantum dots.

We have processed 1.3 µm range InAs quantum dot oxide confined vertical cavity surface emitting lasers with top distributed Bragg reflectors contacts, all on GaAs substrate. Our devices exhibit acceptable parameters for 10 Gigabit Ethernet standards. 1275 nm lasing operation is achieved with low operation voltage and low threshold current. We study the threshold current variation with temperature in continuous wave and pulsed operation. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the observation of the strong coupling regime between a single GaAs quantum dot exciton and a microdisk optical mode. Microphotoluminescence is performed at various temperatures between 4 K and 50 K to tune the exciton through the cavity mode. An anticrossing is observed at 30 K with a Vacuum Rabi splitting of 400 ¹eV, twice as large as the individual linewidths. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

It has been recently reported that the electromagnetic properties of pillar microcavities present an intricate and unexpected behavior for diameters smaller than the resonant wavelength. For instance, the micropillar quality factors can reach values well in excess of the quality factor of the reference planar cavity. In this work, we explain the reason for this behavior and provide an in-depth analysis of the energy-transfer mechanism through distributed Bragg mirror with finite lengths. We show that, in addition to a classical backscattering via the evanescent fundamental Bloch mode, the reflection is also mediated by another Bloch mode, which propagates in the mirror without leakage. This Bloch mode plays a central role in the electromagnetic properties of pillar microcavities and has to be taken into account for the optimization of the micropillar parameters.

We present the experimental evidence of giant optical anisotropy in single InAs QDs. Polarization-resolved photoluminescence spectroscopy in single QDs reveals a linear polarization ratio which fluctuates, from one dot to another, in sign and in magnitude with absolute values up to 82%. We do not observe any dependence of the linear polarization on incident power and temperature.

Two monolayers of CdSe sandwiched by ZnSe layers were grown by molecular-beam epitaxy on a vicinal GaAs surface substrate. Small ensembles of these self-assembled quantum dots (QD) have been studied at low temperatures using micro-photoluminescence spectroscopy. We observe reversible spectral diffusion in individual QD luminescence lines. The energy shift is negligibly small at low optical excitation power and amount to about 0.7 meV under higher excitation (0.6 kW/cm2). Because the energy shift is found to be significantly smaller than the exciton–biexciton splitting of CdSe QDs even under high excitation, the conventional spectral filtering could be used to effectively select the exciton-related emission from these QDs.

The correlation between the photons emitted by an optically pumped single quantum dot is investigated. The correlation function on a single dot isolated in a mesa shows that only one photon is emitted at a time at the exciton frequency. These quantum states of light can be generated with a high quantum efficiency, with the use of cavity effects: surrounding the dot by a pillar microcavity not only increases significantly the single photon flux but also allows the preparation of single photons all in the same quantum state (same spatial mode and same polarization). © 2002 Published by Elsevier Science B.V.

We report decoherence time measurements on the fundamental transition in single InGaAs quantum dots (QDs) by using a high-sensitivity Fourier transform spectroscopy on the photoluminescence signal arising from single QDs. We have investigated two samples with different nature of the wetting layer resulting in different confinement energies. We bring evidence of environment effects on the acoustic phonon assisted broadening processes.

The correlation between the photons emitted by an optically pumped single quantum dot is investigated. The correlation function on a single dot isolated in a mesa shows that only one photon is emitted at a time at the exciton frequency. Moreover, cross-correlation experiments provide evidence of the sequential de-excitation of the quantum dot, yielding a radiative cascade that produces two single photons with a definite order. These quantum states of light can be generated with a high quantum efficiency, with the use of cavity effects: surrounding the dot by a pillar microcavity not only increases significantly the single photon flux but also allows the preparation of single photon all in the same quantum state (same spatial mode and same polarization).

We investigate theoretically the generation of indistinguishable single photons from a strongly dissipative quantum system placed inside an optical cavity. The degree of indistinguishability of photons emitted by the cavity is calculated as a function of the emitter-cavity coupling strength and the cavity linewidth. For a quantum emitter subject to strong pure dephasing, our calculations reveal that an unconventional regime of high indistinguishability can be reached for moderate emittercavity coupling strengths and high quality factor cavities. In this regime, the broad spectrum of a dissipative quantum system is funneled into the narrow lineshape of a cavity. The associated efficiency is found to greatly surpass spectral filtering effects. Our findings open the path towards on-chip scalable indistinguishable-photon emitting devices operating at room temperature., Comment: Main paper (6 pages, 3 figures)+ supplemental materials (4 pages)

We have studied the spin dynamics in nonintentionally doped and n-modulation doped self-organized InAs/GaAs quantum dots (QD) by time-resolved photoluminescence. Under strictly resonant excitation, we demonstrate that the carrier spins in these nanostructures are totally frozen on the neutral or charged exciton lifetime scale. In addition, we show that the spin state of the resident electron in n-doped self-assembled InAs–GaAs QD can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counter-polarized photoluminescence in such structures.

We report the observation of an efficient photoluminescence up-conversion in single InAs/GaAs quantum dots by micro-photoluminescence measurements under cw-excitation. Power dependent measurements show a nearly quadratic dependence of the up-converted photoluminescence signal from the quantum dots (QDs). The intermediate states that allow the efficient photoluminescence up-conversion are deep electronic states located at the vicinity of the QDs. This observation of photoluminescence up-conversion demonstrates the influence on the quantum dot properties of its environment.

We present measurements of electronic spin relaxation and manipulation in n-doped semiconductor quantum dots. A luminescence based nonresonant pump-probe method has been developed to determine the degree of spin polarization of electrons confined in the dots. We observe an electronic spin memory effect up to 20 ns . The mechanism of spin polarization and relaxation are thoroughly analyzed both by continuous wave and time resolved nonresonant luminescence.

We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics, in which the pathways by which the source may emit a photon are restricted, thus channeling emission into one desired mode. Second are those where we try to reshape the free space modes into a target mode in an optimal way, by means of refraction, without fundamentally altering the way in which the source emits. Respectively, we examine a variety of microcavities and solid immersion lenses. Whilst we find that the micropillar microcavities offer the highest collection efficiency (∼70%), choosing this approach may not always be appropriate due to other constraints. Details of the different approaches, their merits and drawbacks are discussed in detail.

International audience; We review the recent development of high efficiency single photon sources based on a single quantum dot in a photonic wire. Unlike cavity-based devices, very pure single photon emission and efficiencies exceeding 0.7 photon per pulse are jointly demonstrated under non-resonant pumping conditions. By placing a tip-shaped or trumpet-like tapering at the output end of the wire, a highly directional Gaussian far-field emission pattern is obtained. More generally, a photonic wire containing a quantum dot appears as an attractive template to explore and exploit in a solid-state system the unique optical properties of "one-dimensional atoms".

We report the development of a light source delivering triggered single photons, based on a single InAs quantum dot embedded in a micropillar cavity. The single photon emission emerging from a single quantum dot is characterized by a strong antibunching in photon correlation measurements. We also demonstrate that an efficient collection of the single photon train can be achieved by exploiting the coupling of the emission into high Q modes of a micropillar cavity. Moreover, we show that the coupling to polarized cavity modes permits quantum state preparation (same spatial mode and same polarization) of the single photons.

Spontaneous emission (SE) control in the solid state has been extensively studied for about 10 years as a route toward optoelectronic devices with improved properties or novel functionalities. Thanks to their atom-like emission and to their relatively large oscillator strength, InGaAs/GaAs semiconductor quantum boxes (QBs) open revolutionary opportunities for the application of the concepts of cavity quantum electrodynamics in monolithic microcavities. Such emitters experience in particular a very large enhancement of their spontaneous emission rate (Purcell effect) when inserted in high Q /low volume micropillars (×5) or microdisks (×15). This result opens unique opportunities for the development of solid-state photon guns, able to emit single-photon pulses in a deterministic way. QBs in microdisks should also allow in the near future to achieve a strong coupling regime for a single solid-state emitter.

We present an experimental study of the main modes involved in the emission properties of InGaAs-GaAs quantum-well oxide-confined long wavelength vertical-cavity surface-emitting lasers. Lasing properties are dominated by the so-called "oxide modes" and by aperture modes, respectively, for small and large driving currents. We present complementary investigations of the laser emission including far-field angular distribution and spectroscopic near-field optical microscopy to a better understanding of the nature of the "oxide modes".

In a Quantum Well embedded in a planar optical microcavity, excitons can be strongly coupled to the electromagnetic standing wave and form 2D polaritons. If N Quantum Wells are placed in the microcavity, they cooperate to a collective polariton state. The luminescence dynamics under resonant excitation is modified by the cavity and varies continuously with the detuning between the exciton and the cavity mode. However, since only 10 % of the exciton radiant states are in the strong coupling regime, as soon as scattering by acoustic phonons has occurred, mainly states in the weak coupling regime are populated and govern the luminescence dynamics, As a consequence, cavity effects are significant only under resonant excitation and for short time delays. To improve the modifications of spontaneous emission, it seems promising to study pillar microcavities where the light is confined in all directions and could be strongly coupled to a larger fraction of exciton states.

We study, by time-resolved photoluminescence, the radiative lifetime of InAs quantum boxes (QBs) placed in the core of small volume and high finesse GaAs/AlAs pillar microresonators. The spontaneous emission rate of the QBs, which are on-resonance with a cavity mode, is found to be up to five time larger than for QBs which are off-resonance. We explain this effect by considering the modification of the vacuum electromagnetic field induced by the cavity.

Semiconductor quantum boxes (QB's) are well suited to cavity quantum electrodynamic experiments in the solid state because of their sharp emission. We study by time-resolved photoluminescence InAs QB's placed in the core of small-volume and high-finesse GaAs/AlAs pillar microresonators. A spontaneous emission rate enhancement by a factor of up to 5 is selectively observed for the QB's which are on resonance with one-cavity mode. We explain its magnitude by considering the Purcell figure of merit of the micropillars and the effect of the random spatial and spectral distributions of the QB's.

GaAs/AlAs pillar microcavities containing an array of InAs quantum boxes in their core region have been fabricated by molecular beam epitaxy, electron-beam lithography and reactive ion etching. By placing this broadband light emitter in the cavity, we can probe precisely by photoluminescence the modal structure of the micropillars. After having validated this approach through the study of circular pillars, we address two important issues in context of spontaneous emission control. We show first that it is possible, by choosing an elliptical cross-section, to lift the polarization degeneracy of the fundamental mode of circular micropillars. By measuring Purcell’s factor for small pillars containing quantum boxes, we then highlight their potential for observing large cavity quantum electrodynamic effects in the weak coupling regime, which is confirmed by recent preliminary time-resolved experiments.