Quantum correlations of two optical fields close to electromagnetically induced transparency

We show that three-level atoms excited by two cavity modes in a $\Lambda$ configuration close to electromagnetically induced transparency can produce strongly squeezed bright beams or correlated beams which can be used for quantum non demolition measurements. The input intensity is the experimental "knob" for tuning the system into a squeezer or a quantum non demolition device. The quantum correlations become ideal at a critical point characterized by the appearance of a switching behavior in the mean fields intensities. Our predictions, based on a realistic fully quantum 3-level model including cavity losses and spontaneous emission, allow direct comparison with future experiments.Comment: 4 pages, 5 figure

Pure emitter dephasing : a resource for advanced solid-state single photon sources

We have computed the spectrum emitted spontaneously by a quantum dot coupled to an arbitrarily detuned single mode cavity, taking into account pure dephasing processes. We show that if the emitter is incoherent, the cavity can efficiently emit photons with its own spectral characteristics. This effect opens unique opportunities for the development of devices exploiting both cavity quantum electrodynamics effects and pure dephasing, such as wavelength stabilized single photon sources robust against spectral diffusion.Comment: 5 pages, 3 figure

Improving teleportation of continuous variables by local operations

We study a continuous-variable (CV) teleportation protocol based on a shared entangled state produced by the quantum-nondemolition (QND) interaction of two vacuum states. The scheme utilizes the QND interaction or an unbalanced beam splitter in the Bell measurement. It is shown that in the non-unity gain regime the signal transfer coefficient can be enhanced while the conditional variance product remains preserved by applying appropriate local squeezing operation on sender's part of the shared entangled state. In the unity gain regime it is demonstrated that the fidelity of teleportation can be increased with the help of the local squeezing operations on parts of the shared entangled state that convert effectively our scheme to the standard CV teleportation scheme. Further, it is proved analytically that such a choice of the local symplectic operations minimizes the noise by which the mean number of photons in the input state is increased during the teleportation. Finally, our analysis reveals that the local symplectic operation on sender's side can be integrated into the Bell measurement if the interaction constant of the interaction in the Bell measurement can be adjusted properly.Comment: 10 pages, 1 figure, discussion of the non-unity gain teleportation is adde

Twin polaritons in semiconductor microcavities

The quantum correlations between the beams generated by polariton pair scattering in a semiconductor microcavity above the parametric oscillation threshold are computed analytically. The influence of various parameters like the cavity-exciton detuning, the intensity mismatch between the signal and idler beams and the amount of spurious noise is analyzed. We show that very strong quantum correlations between the signal and idler polaritons can be achieved. The quantum effects on the outgoing light fields are strongly reduced due to the large mismatch in the coupling of the signal and idler polaritons to the external photons

Correlated Photon Emission from a Single II-VI Quantum Dot

We report correlation and cross-correlation measurements of photons emitted under continuous wave excitation by a single II-VI quantum dot (QD) grown by molecular-beam epitaxy. A standard technique of microphotoluminescence combined with an ultrafast photon correlation set-up allowed us to see an antibunching effect on photons emitted by excitons recombining in a single CdTe/ZnTe QD, as well as cross-correlation within the biexciton ($X_{2}$)-exciton ($X$) radiative cascade from the same dot. Fast microchannel plate photomultipliers and a time-correlated single photon module gave us an overall temporal resolution of 140 ps better than the typical exciton lifetime in II-VI QDs of about 250ps.Comment: 4 pages, 3 figures, to appear in Appl. Phys. Let

Caractérisation des modes de coordination interpersonnelle au sein d'une équipe de basket-ball

Characterization of interpersonal coordination modes within a basket-ball team. The aim of our study was to analyze the construction of a collective activity. We focused on interpersonal coordination process within a basket-ball team during a match. We characterized the way how basketball players took mutually into account their respective activities. In order to consider in the same time both units of analysis, the individual one and the collective one, this study referred to the framework of the course of action theory (Theureau, 2006). Results allowed us to specify the relational network between players, the various coordination modes between two players and the different forms of team coordination. These results are discussed with regard to the nature of interactions within the team, and with regard to the notion of a collective action plan : they highlighted that some collective activity construction modalities are based on local overlapping coordination. These results thus question the status of a collective plan (as a scheme shared by all the players).Caractérisation de modes de coordination interpersonnels dans une équipe de basket-ball. Le but de notre étude était d'analyser la construction d'une activité collective. Nous nous sommes concentrés sur le processus de coordination interpersonnel dans une équipe de basket-ball pendant un match(une allumette). Nous avons caractérisé la voie comment les basketteurs ont pris mutuellement en considération leurs activités respectives. Pour considérer dans le même temps les deux unités d'analyse, le individuel et le collectif, cette étude a mentionné la structure du cours de théorie d'action (Theureau, 2006). Les résultats nous ont permis de spécifier le réseau relationnel entre des acteurs(joueurs), les modes de coordination divers entre deux acteurs(joueurs) et les formes(formulaires) différentes de coordination d'équipe. Ces résultats sont discutés en ce qui concerne la nature d'interactions dans l'équipe et en ce qui concerne la notion d'un plan d'action collectif : ils ont mis en évidence(ont surligné) ces quelques modalités de construction d'activité collectives sont basé sur la coordination de chevauchement locale. Ces résultats mettent ainsi en doute le statut d'un plan collectif (comme un plan(arrangement) partagé par tous les acteurs(joueurs))

Monitoring stimulated emission at the single photon level in one-dimensional atoms

We theoretically investigate signatures of stimulated emission at the single photon level for a two-level atom interacting with a one-dimensional light field. We consider the transient regime where the atom is initially excited, and the steady state regime where the atom is continuously driven with an external pump. The influence of pure dephasing is studied, clearly showing that these effects can be evidenced with state of the art solid state devices. We finally propose a scheme to demonstrate the stimulation of one optical transition by monitoring another one, in three-level one-dimensional atoms.Comment: 4 pages, 4 figures. Improved introduction; Comments adde

Room temperature stable single-photon source

We report on the realization of a stable solid state room temperature source for single photons. It is based on the fluorescence of a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. Antibunching has been observed in the fluorescence light under both continuous and pulsed excitation. Our source delivers 2*10^4 single-photon pulses per second at an excitation repetition rate of 10 MHz. The number of two-photon pulses is reduced by a factor of five compared to strongly attenuated coherent sources.Comment: 7 pages, 10 figures, accepted to the special issue of the European Physical Journal D on "Quantum interference and cryptographic keys: novel physics and advancing technologies", proceedings of the conference QUICK 200

Conditional preparation of a quantum state in the continuous variable regime: generation of a sub-Poissonian state from twin beams

We report the first experimental demonstration of conditional preparation of a non classical state of light in the continuous variable regime. Starting from a non degenerate OPO which generates above threshold quantum intensity correlated signal and idler "twin beams", we keep the recorded values of the signal intensity only when the idler falls inside a band of values narrower than its standard deviation. By this very simple technique, we generate a sub-Poissonian state 4.4dB below shot noise from twin beams exhibiting 7.5dB of noise reduction in the intensity difference.Comment: 4 pages, Accepted in Phys. Rev. Let