1,721,025 research outputs found
Photon lasing in GaAs microcavity: Similarities with a polariton condensate
No full textWe study experimentally the lasing regime of a GaAs based microcavity sample under strong optical pumping. The very same sample exhibits the strong coupling regime at low excitation power with a Rabi splitting as large as 15 meV. We show that some features which may be considered as experimental evidence of polariton Bose-Einstein condensation are also observed in the weak coupling regime when the cavity is behaving as a regular photon laser. In particular, the emission pattern in the lasing regime displays a sharp peak near the energy minimum followed by a Boltzmann distribution at higher energies
Polariton light-emitting diode in a GaAs-based microcavity
No full textCavity polaritons have been shown these last years to exhibit a rich variety of nonlinear behaviors which could be used in new polariton based devices. Operation in the strong coupling regime under electrical injection remains a key step toward a practical polariton device. We report here on the realization of a polariton based light-emitting diode using a GaAs microcavity with doped Bragg mirrors. Both photocurrent and electroluminescence spectra are governed by cavity polaritons up to 100 K
Polariton laser using single micropillar GaAs-GaAlAs semiconductor cavities
No full textPolariton lasing is demonstrated on the zero-dimensional states of single GaAs=GaAlAs micropillar
cavities. Under nonresonant excitation, the measured polariton ground-state occupancy is found as large
as 10^4. Changing the spatial excitation conditions, competition between several polariton lasing modes is
observed, ruling out Bose-Einstein condensation. When the polariton state occupancy increases, the
emission blueshift is the signature of self-interaction within the half-light half-matter polariton lasing
mode
Spontaneous formation of a polariton condensate in a planar GaAs microcavity
No full textWe report on polariton condensation in a planar GaAs microcavity under nonresonant optical excitation. Angularly resolved photoluminescence measurements demonstrate polariton condensation for temperature up to 40 K. Numerical simulations using Boltzmann equations give an overall description of the observed condensation for various detunings and temperatures. This model highlights the importance of the polariton relaxation rate as compared to the polariton decay for condensation to occur on the lowest energy polariton states
Optical Bistability in a GaAs-Based Polariton Diode
No full textWe report on a new type of optical nonlinearity in a polariton p-i-n microcavity. Abrupt switching between the strong and weak coupling regime is induced by controlling the electric field within the cavity. As a consequence, bistable cycles are observed for low optical powers (2–3 orders of magnitude less than for Kerr induced bistability). Signatures of switching fronts propagating through the whole 300 x 300 um^2 mesa surface are evidenced
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Impact de la cohérence dans la base d'états de nombre de photons sur les performances et aspects énergétiques des protocoles d'optique quantique
No full textLes émetteurs quantiques sont des sources de photons uniques intéressantes pour les technologies quantiques, pouvant théoriquement émettre un photon unique sur demande. En 2019, il a été démontré que sous excitation résonnante, la cohérence imprimée entre l'état fondamental et l'état excité de l'émetteur quantique est transférée lors de l'émission spontanée en cohérence dans la base d'états de nombre de photons, créant une superposition cohérente de zéro et un photon. Cette démonstration a conduit à de nouvelles études théoriques sur le rôle de la cohérence en nombre de photons en optique quantique et en thermodynamique quantique. Dans cette thèse, nous étudions expérimentalement l'impact de la cohérence en nombre de photons sur certains fondamentaux de l'optique quantique - par exemple l'effet Hong-Ou-Mandel et les interférences de Ramsey - du point de vue de l'optique quantique et de la thermodynamique quantique. Nous démontrons que la cohérence en nombre de photons doit être prise en compte lors de la réalisation de mesures d'indiscernabilité et peut conduire à de nouveaux phénomènes d'interférence quantique qui peuvent altérer considérablement les performances de portes quantiques annoncées. Par ailleurs, nous démontrons que la cohérence occupe non seulement une place centrale en optique quantique, mais aussi dans le domaine de la thermodynamique quantique en proposant et mettant en œuvre des protocoles expérimentaux afin de mesurer les échanges énergétiques entre un émetteur quantique et la lumière. Nous montrons que la génération de cohérence dans un émetteur quantique peut conduire à un transfert spontané de travail vers le champ électromagnétique, qui est réduite par la décohérence de l'émetteur ainsi que par intrication cumulée émetteur-champ lors de l'émission spontanée. Cette dernière observation est approfondie en étudiant les transferts énergétiques entre un émetteur quantique et le vide du champ électromagnétique lors de l'interférence de Ramsey. Cette thèse pose ainsi les bases pour de nombreuses autres études expérimentales sur l'impact et l'utilisation des états de superposition en nombre de photons dans les protocoles d'optique quantique et l'énergétique de l'informatique quantique optique.Quantum emitters are interesting single-photon sources for quantum technologies that can theoretically emit a single-photon on-demand. In 2019 it was shown that when resonantly excited, the coherence imprinted on the quantum emitter in the energy basis is mapped upon spontaneous emission onto coherence in the photon-number basis, creating a coherent photon-number superposition of zero- and one-photon. This demonstration led to new theoretical investigations on the role of photon-number coherence in quantum optics and quantum thermodynamics. In this thesis we experimentally study the impact of photon-number coherence on pillars of quantum optics -- e.g. the Hong-Ou-Mandel effect and the Ramsey sequence -- from a quantum optics and quantum thermodynamics perspective. We demonstrate that photon-number coherence has to be considered when performing indistinguishability measurements and can lead to new quantum interference phenomena that can substantially alter the performances of heralded quantum gates. Additionally, we demonstrate that coherence not only takes a pivotal place in quantum optics, but also in the field of quantum thermodynamics by proposing and implementing experimental protocols to measure energetic exchanges between a quantum emitter and light fields. We show that the generation of coherence in a quantum emitter can lead to the spontaneous release of work in the electromagnetic field, which is reduced by decoherence and the build-up of emitter-field entanglement during spontaneous emission. The latter observation is further exploited by studying the energetic transfers between a quantum emitter and the vacuum of the electromagnetic field along the Ramsey sequence. This thesis serves as the first steps to hopefully many more experimental studies into the impact and use of photon-number superposition states and photon-number coherence in quantum optics protocols and the energetics of optical quantum computing
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