Indistinguishable near infra-red single photons from an individual organic molecule

By using the zero-phonon line emission of an individual organic molecule, we realized a source of indistinguishable single photons in the near infrared. A Hong-Ou-Mandel interference experiment is performed and a two-photon coalescence probability of higher than 50% at 2 K is obtained. The contribution of the temperature-dependent dephasing processes to the two-photon interference contrast is studied. We show that the molecule delivers nearly ideal indistinguishable single photons at the lowest temperatures when the dephasing is nearly lifetime limited. This source is used to generate post-selected polarization-entangled photon pairs, as a test-bench for applications in quantum information

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Indistinguishable near infra-red single photons from an individual organic molecule

Over the past decade, the quest for photon-based quantum information processing schemes has fueled interest in multiphoton interference phenomena. In particular, linear optics quantum computation and quantum teleportation require the effect of two-photon quantum interference between single photons on a beam-splitter. Ideally, a light source that delivers on demand single photons with similar wavepackets is desired for these applications. The indistinguishability of the photons generated by single quantum emitters was tested with two photon quantum interference, for different test-bench systems like trapped atoms or ions in the gas phase. Yet, these systems suffer from weak duty cycles or low light collection efficiency, as well as challenging methods for scaling to large numbers of emitters. Solid-state emitters such as semiconductor quantum dots were used to demonstrate the photon coalescence and to produce post-selected entangled states, but they usually display residual dephasing and spectral diffusion processes which spoil the coherence properties of the emitted photons. Individual fluorescent molecules in solids are another promising alternative for single photon generation. At liquid helium temperatures and for well chosen fluorophore-matrix systems, dephasing of the transition dipole due to phonons is drastically reduced. Such molecules behave like two-level systems with a fluorescence quantum yield close to unity, thus offering optical properties similar to those of trapped single atoms. Moreover, the photostability of organic molecules trapped in crystalline hosts is excellent at cryogenic temperatures, and allows continuous optical measurements over days. Using the zero-phonon line emission of an individual organic molecule, we realized a source of indistinguishable single photons in the near infrared. We performed a Hong-Ou-Mandel coalescence experiment and we observed a two-photon interference contrast as high as 50% at 2 K comparable to values obtained for self-assembled quantum dots in microcavity structures. This analysis suggests that dephasing of the molecular transition dipole due to phonons in the crystalline matrix is negligible at 2 K, enabling a single DBT molecule to deliver indistinguishable single photons. Yet, a quantitative study of the photon coalescence degradation by dephasing processes is required to verify the potentialities of this single photon source in quantum information processing. We quantitatively studied the photon coalescence degradation by dephasing processes due to the finite temperature of the matrix host, and we show that the coalescence efficiency drops by a factor of ten upon increasing the temperature from 2 K to 5 K. We show that this lost of coherence is in agreement with the temperature dependence of the ZPL widths

Optical Nanoscopy with Excited State Saturation at Liquid Helium Temperatures

International audienc

Microscopie STED en champ large à l'aide de réseaux optiques et microscopie STED confocal à température cryogénique

séminaire invité ESPCILes récents développements en microscopie super-résolue (PALM, STORM, RESOLFT, STED, ... ) ont permis d'atteindre des résolutions optiques nanométriques. Les premières méthodes (PALM, STORM, RESOLFT) sont dites de super-localisation. Elles nécessitent une densité faible de molécules émettant des photons afin de pouvoir pointer le centre de chacune d'entre elles indépendamment. Malgré une imagerie en champ large, ces techniques requièrent l'acquisition d'un nombre important d'images pour reconstruire une image super-résolue, ce qui limite fortement la cadence de génération des images. La microscopie STED est quant à elle une méthode d'imagerie confocale qui ne nécessite aucun post-traitement contrairement aux précédentes mais qui reste néanmoins lente par son type d'acquisition (enregistrement point par point). Pour accélérer cette cadence, nous avons parallélisé la méthode à l'aide de 100 points de mesure en utilisant un réseau optique pour l'excitation et la déplétion des fluorophores et d'une caméra CMOS pour la détection. Dans ces conditions, nous avons obtenues des images super-résolues (résolution de 70 nm) avec des billes fluorescentes de 20 nm de diamètre sur des champs de 3*3 μm2 et avons pu suivre la dynamique de diffusion de ces billes dans un gel de polymère à une cadence de 12.5 images/s. Nous avons également appliqué cette méthode à des échantillons biologiques (microtubules) . Dans une seconde partie, je montrerais qu'à température cryogénique, il est possible d'atteindre une résolution optique aussi petite que 5 nm pour des puissances optiques très modérées (seulement 100 μW). Cette nouvelle méthode permet d'envisager l'étude du couplage dipôle-dipôle en deux molécules organiques

L'optique quantique avec des molécules uniques

Séminaire Institut d'Optique Palaiseau du 1 mars 201

Etude de gaz quantiques dégénérés quasi-unidimensionnels confinés par une micro-structure

This thesis presents experiments on degenerate Bose gases in the quasi-one dimensional regime. For this purpose we use an atom chip, microfabricated wires deposited on surfaces, to create very anisotropic traps in which we measured the statistical properties of an ultracold bosonic gas (Rubidium 87). For a classical gas, where the particles are statistically independent, density fluctuations are given by the atomic shot noise. At lower temperatures, the quantum nature of the particles appears (indistinguishable bosons), and an extra term has to be taken into account to describe the bosonic bunching. At low atomic densities, we observe these two kinds of behavior in good agreement with the ideal Bose gas predictions. At higher atomic densities, due to the energy cost of inter-atomic repulsive interactions, we observed a reduction of density fluctuations compared to the ideal case. This reduction reflects the transition to the quasi-condensate regime. To exploit the full potential of atom chip, atoms must often be close to the material structures which confine them. However, this proximity renders these devices highly sensitive to defects which produce roughness in the trapping potential. To circumvent this problem, we used a time-dependent trap where the atoms see the time-averaged potential without any roughness.Cette thèse présente l'étude et la réalisation expérimentale de gaz de bosons dégénérés quasi-unidimensionnels. Pour atteindre ce type de régime, nous utilisons une puce atomique, micro-fils d'or déposés sur un substrat de silicium qui permet de créer des pièges magnétiques très anisotropes dans lesquels nous avons mesuré les propriétés statistiques de gaz de bosons ultra-froids (Rubidium 87). Pour un gaz classique, où les particules sont statistiquement indépendantes, les fluctuations de densité sont données par le bruit de grenaille atomique. A plus basse température, la nature quantique des particules (bosons indiscernables) doit être prise en compte et des fluctuations de densité supplémentaires apparaissent dues au phénomène de groupement de bosons. A faibles densités atomiques, nous avons observé ces deux types de comportements en bon accord avec le comportement du gaz idéal. A plus fortes densités, à cause des interactions répulsives entre atomes qui sont coûteuses en énergie, nous avons observé une réduction des fluctuations de densité par rapport au gaz idéal. Cette réduction est caractéristique de la transition vers un quasi-condensat. Pour exploiter pleinement le potentiel des puces à atomes, les atomes doivent être situés aux abords des micro-structures qui les piègent. Cependant, cette proximité rend ces dispositifs sensibles aux imperfections de microfabrication en introduisant une rugosité non contrôlée sur le potentiel de piégeage. Pour contourner ce problème, nous avons mis au point une méthode pour s'affranchir de ce problème en modulant rapidement le courant des micro-fils. Les atomes sont alors soumis à un potentiel moyen effectif exempt de rugosité

Le métier de chercheur

Carrefour des Métiers au lycée Montesquieu de Bordeau