Photon correlations in the collective emission of hybrid gold-(CdSe/CdS/CdZnS) nanocrystal supraparticles.

We investigate the photon statistics of the light emitted by single self-assembled hybrid gold-CdSe/CdS/CdZnS colloidal nanocrystal supraparticles through the detailed analysis of the intensity autocorrelation functiong(2)(τ). We first reveal that, despite the large number of nanocrystals involved in the supraparticle emission, antibunching can be observed. We then present a model based on non-coherent Förster energy transfer and Auger recombination that well captures photon antibunching. Finally, we demonstrate that some supraparticles exhibit a bunching effect at short time scales corresponding to coherent collective emission.

Fluorescence decay enhancement and FRET inhibition in self-assembled hybrid gold CdSe/CdS/CdZnS colloidal nanocrystal supraparticles.

We report on the synthesis of hybrid light emitting particles with a diameter ranging between 100 and 500 nm, consisting in a compact semiconductor CdSe/CdS/CdZnS nanocrystal aggregate encapsulated by a controlled nanometric size silica and gold layers. We first characterize the Purcell decay rate enhancement corresponding to the addition of the gold nanoshell as a function of the particle size and find a good agreement with the predictions of numerical simulations. Then, we show that the contribution corresponding to Förster resonance energy transfer is inhibited.

Superradiant Emission from a Collective Excitation in a Semiconductor.

We report an anomalous wide broadening of the emission spectra of an electronic excitation confined in a two-dimensional potential. We attribute these results to an extremely fast radiative decay rate associated with superradiant emission from the ensemble of confined electrons. Lifetimes extracted from the spectra are below 100 fs and, thus, 6 orders of magnitude faster than for single particle transitions at similar wavelength. Moreover, the spontaneous emission rate increases with the electronic density, as expected for superradiant emission. The data, all taken at 300 K, are in excellent agreement with our theoretical model, which takes into account dipole-dipole Coulomb interaction between electronic excitations. Our experimental results demonstrate that the interaction with infrared light, which is usually considered a weak perturbation, can be a very efficient relaxation mechanism for collective electronic excitations in solids.

[Anti-rotavirus vaccination: what impedes its wide prescription]. / Quels sont les freins à la vaccination contre le rotavirus ? Enquête auprès des médecins généralistes et pédiatres de la communauté urbaine de Bordeaux.

UNLABELLED: The aim of this study was to analyze why anti-rotavirus vaccination is rarely used in France, although this infection is frequent and associated with a large number of hospitalizations. METHOD: A questionnaire was sent to 732 general practitioners and pediatricians in the Bordeaux area. RESULTS: The response rate was 57% (381 GPs and 38 pediatricians). Most of them (71.8%) declared that they received information on the vaccination and more than 80% of them feel that gastroenteritis is a severe disease. However, anti-rotavirus is never prescribed by the majority of them (59.6%) and only 2.6% prescribe it systematically. The reasons are that the patient is not refunded (64.2%), the vaccination timetable is overloaded (53.6%), and there are no recommendations for this vaccination (35.1%). Physicians believe that parents feel gastroenteritis as a benign disease (52.6%) and say that they refuse the vaccination because it is not refunded (77.7%), not mandatory (45.5%), or may have side effects (44.1%). Physicians' prescription of vaccination is correlated to their information on the vaccination and their feeling about the disease's severity. They would modify their practice if the vaccination was recommended and/or refunded. CONCLUSION: The main obstacles against anti-rotavirus vaccination are the absence of recommendations and refunding. The recent recommendation for the vaccination and a lower price should lead to its generalization in France.

Quantum teleportation from a propagating photon to a solid-state spin qubit.

A quantum interface between a propagating photon used to transmit quantum information and a long-lived qubit used for storage is of central interest in quantum information science. A method for implementing such an interface between dissimilar qubits is quantum teleportation. Here we experimentally demonstrate transfer of quantum information carried by a photon to a semiconductor spin using quantum teleportation. In our experiment, a single photon in a superposition state is generated using resonant excitation of a neutral dot. To teleport this photonic qubit, we generate an entangled spin-photon state in a second dot located 5 m away and interfere the photons from the two dots in a Hong-Ou-Mandel set-up. Thanks to an unprecedented degree of photon-indistinguishability, a coincidence detection at the output of the interferometer heralds successful teleportation, which we verify by measuring the resulting spin state after prolonging its coherence time by optical spin-echo.

Charge-induced coherence between intersubband plasmons in a quantum structure.

In this Letter we investigate a low dimensional semiconductor system, in which the light-matter interaction is enhanced by the cooperative behavior of a large number of dipolar oscillators, at different frequencies, mutually phase locked by Coulomb interaction. We experimentally and theoretically demonstrate that, owing to this phenomenon, the optical response of a semiconductor quantum well with several occupied subbands is a single sharp resonance, associated with the excitation of a bright multisubband plasmon. This effect illustrates how the whole oscillator strength of a two-dimensional system can be concentrated into a single resonance independently from the shape of the confining potential. When this cooperative excitation is tuned in resonance with a cavity mode, their coupling strength can be increased monotonically with the electronic density, allowing the achievement of the ultrastrong coupling regime up to room temperature.