Superfluidity of polaritons in semiconductor microcavities

Superfluidity, the ability of a quantum fluid to flow without friction, is one of the most spectacular phenomena occurring in degenerate gases of interacting bosons. Since its first discovery in liquid helium-4 (refs 1, 2), superfluidity has been observed in quite different systems, and recent experiments with ultracold trapped atoms have explored the subtle links between superfluidity and Bose-Einstein condensation(3-5). In solid-state systems, it has been anticipated that exciton polaritons in semiconductor microcavities should behave as an unusual quantum fluid(6-8), with unique properties stemming from its intrinsically non-equilibrium nature. This has stimulated the quest for an experimental demonstration of superfluidity effects in polariton systems(9-13). Here, we report clear evidence for superfluid motion of polaritons. Superfluidity is investigated in terms of the Landau criterion and manifests itself as the suppression of scattering from defects when the flow velocity is slower than the speed of sound in the fluid. Moreover, a. Cerenkov-like wake pattern is observed when the flow velocity exceeds the speed of sound. The experimental findings are in quantitative agreement with predictions based on a generalized Gross-Pitaevskii theory(12,13), and establish microcavity polaritons as a system for exploring the rich physics of non-equilibrium quantum fluids

Observation of Superfluidity of Polaritons in Semiconductor Microcavities

One of the most striking manifestations of quantum coherence in interacting boson systems is superfluidity. Exciton-polaritons in semiconductor microcavities are two-dimensional composite bosons predicted to behave as particular quantum fluids. We report the observation of superfluid motion of polaritons created by a laser in a semiconductor microcavity. Superfluidity is investigated in terms of the Landau criterion and manifests itself as the suppression of scattering from defects when the flow velocity is slower than the speed of sound in the fluid. On the other hand, a Cerenkov-like wake pattern is clearly observed when the flow velocity exceeds the speed of sound. The experimental findings are in excellent quantitative agreement with the predictions based on a generalized Gross-Pitaevskii theory, showing that polaritons in microcavities constitute a very rich system for exploring the physics of non-equilibrium quantum fluids.Comment: 14 pages, 3 figure

Polaritons en microcavité semi-conductrice : dynamique de fluide quantique, effets de spin et mesures de bruit en régime d'oscillation paramétrique

This work is devoted to the study of the properties of polaritons, half-matter/half-light particles, in a semiconductor microcavity. Their bosonic behaviour enables to reach macroscopic coherence regimes such as Bose-Einstein condensation and super uflidity which we have experimentally demonstrated. We also developed a way to optically engineer the polariton landscape by creating arti cial defects on the sample, which will help finding some fancy behaviours such as turbulence. Thanks to the strong spin-dependant interactions between polaritons and the very high propagation speeds due to their photonic component, we could build an all-optical, ultra-fast spin switch device operating at low injected power. We managed to control the spatial distribution in spin of the polaritonic beam and con fine a pure spin state within a micrometer-sized region. The bistability of the system led us to reconsider the sign of the interaction constant between cross-polarized polaritons. Finally, we carried on investigating the possibility of generating twin photons in the parametric oscillation regime by four-wave mixing, with correlations measures and transverse-mode noise distribution analysis, in di fferent planar cavity types and in micropillars (0D).Ce travail est consacré à l'étude des propriétés des polaritons, particules mi-lumière mi-matière, en microcavité semi-conductrice. Leur caractère bosonique autorise l'accès à des régimes de cohérence macroscopique tels la condensation de Bose-Einstein et la superfl uidité que nous avons démontrée expérimentalement. Nous avons également développé une technique permettant de modifier optiquement l'environnement polaritonique par création de défauts arti ficiels, ce qui facilite l'obtention de comportements particuliers du fluide polaritonique comme la turbulence. Les fortes interactions dépendantes du spin entre ces particules, alliées à des vitesses de propagation très élevées du fait de leur composante photonique, nous ont permis de réaliser un interrupteur performant contrôlé optiquement, codé en polarisation et en intensité. Nous avons également réussi à manipuler la distribution spatiale en spin d'un faisceau de polaritons, et notamment à confi ner des états de spin pur sur des zones de quelques microns. Le phénomène de bistabilité présent dans le système nous a amené à reconsidérer le signe de la constante d'interaction entre polaritons de spin opposés. En fin, en régime d'oscillation paramétrique par mélange à quatre ondes, nous avons poursuivi l'étude de génération de photons jumeaux grâce à des mesures de corrélations et des analyses en bruit de la distribution modale transverse, dans diff érents types de cavités planaires puis dans des micropiliers (0D)

Polaritons en microcavité semi-conductrice (dynamique de fluide quantique, effts de spin et mesures de bruits en régime d'oscillation paramétrique)

Ce travail est consacré à l'étude des propriétés des polaritons, particules mi-lumière mi-matière, en microcavité semi-conductrice. Leur caractère bosonique autorise l'accès à des régimes de cohérence macroscopique tels la condensation de Bose-Einstein et la superfluidité que nous avons démontrée expérimentalement. Nous avons également développé une technique permettant de modifier optiquement l'environnement polaritonique par création de défauts artificiels, ce qui facilite l'obtention de comportements particuliers du fluide polaritonique comme la turbulence. Les fortes interactions dépendantes du spin entre ces particules, alliées à des vitesses de propagation très élevées du fait de leur composante photonique, nous ont permis de réaliser un interrupteur performant contrôlé optiquement, codé en polarisation et en intensité. Nous avons également réussi à manipuler la distribution spatiale en spin d'un faisceau de polaritons, et notamment à confiner des états de spin pur sur des zones de quelques microns. Le phénomène de bistabilité présent dans le système nous a amené à reconsidérer le signe de la constante d'interaction entre polaritons de spin opposés. Enfin, en régime d'oscillation paramétrique par mélange à quatre ondes, nous avons poursuivi l'étude de génération de photons jumeaux grâce à des mesures de corrélations et des analyses en bruit de la distribution modale transverse, dans différents types de cavités planaires puis dans des micropiliers (0D).PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Genome-wide association study identifies new HLA class II haplotypes strongly protective against narcolepsy.

Contains fulltext : 88508.pdf (publisher's version ) (Closed access)Narcolepsy is a rare sleep disorder with the strongest human leukocyte antigen (HLA) association ever reported. Since the associated HLA-DRB1*1501-DQB1*0602 haplotype is common in the general population (15-25%), it has been suggested that it is almost necessary but not sufficient for developing narcolepsy. To further define the genetic basis of narcolepsy risk, we performed a genome-wide association study (GWAS) in 562 European individuals with narcolepsy (cases) and 702 ethnically matched controls, with independent replication in 370 cases and 495 controls, all heterozygous for DRB1*1501-DQB1*0602. We found association with a protective variant near HLA-DQA2 (rs2858884; P < 3 x 10(-8)). Further analysis revealed that rs2858884 is strongly linked to DRB1*03-DQB1*02 (P < 4 x 10(-43)) and DRB1*1301-DQB1*0603 (P < 3 x 10(-7)). Cases almost never carried a trans DRB1*1301-DQB1*0603 haplotype (odds ratio = 0.02; P < 6 x 10(-14)). This unexpected protective HLA haplotype suggests a virtually causal involvement of the HLA region in narcolepsy susceptibility.1 september 201

DQB1 locus alone explains most of the risk and protection in narcolepsy with cataplexy in Europe

\u3cp\u3eSTUDY OBJECTIVE: Prior research has identified five common genetic variants associated with narcolepsy with cataplexy in Caucasian patients. To replicate and/or extend these findings, we have tested HLA-DQB1, the previously identified 5 variants, and 10 other potential variants in a large European sample of narcolepsy with cataplexy subjects.\u3c/p\u3e\u3cp\u3eDESIGN: Retrospective case-control study.\u3c/p\u3e\u3cp\u3eSETTING: A recent study showed that over 76% of significant genome-wide association variants lie within DNase I hypersensitive sites (DHSs). From our previous GWAS, we identified 30 single nucleotide polymorphisms (SNPs) with P &lt; 10(-4) mapping to DHSs. Ten SNPs tagging these sites, HLADQB1, and all previously reported SNPs significantly associated with narcolepsy were tested for replication.\u3c/p\u3e\u3cp\u3ePATIENTS AND PARTICIPANTS: For GWAS, 1,261 narcolepsy patients and 1,422 HLA-DQB1*06:02-matched controls were included. For HLA study, 1,218 patients and 3,541 controls were included.\u3c/p\u3e\u3cp\u3eMEASUREMENTS AND RESULTS: None of the top variants within DHSs were replicated. Out of the five previously reported SNPs, only rs2858884 within the HLA region (P &lt; 2x10(-9)) and rs1154155 within the TRA locus (P &lt; 2x10(-8)) replicated. DQB1 typing confirmed that DQB1*06:02 confers an extraordinary risk (odds ratio 251). Four protective alleles (DQB1*06:03, odds ratio 0.17, DQB1*05:01, odds ratio 0.56, DQB1*06:09 odds ratio 0.21, DQB1*02 odds ratio 0.76) were also identified.\u3c/p\u3e\u3cp\u3eCONCLUSION: An overwhelming portion of genetic risk for narcolepsy with cataplexy is found at DQB1 locus. Since DQB1*06:02 positive subjects are at 251-fold increase in risk for narcolepsy, and all recent cases of narcolepsy after H1N1 vaccination are positive for this allele, DQB1 genotyping may be relevant to public health policy.\u3c/p\u3