Optical determination and magnetic manipulation of single nitrogen-vacancy color center in diamond nanocrystal

The controlled and coherent manipulation of individual quantum systems is a fundamental key for the development of quantum information processing. The nitrogen-vacancy (NV) color center in diamond is a promising system since its photoluminescence is perfectly stable at room temperature and its electron spin can be optically read-out at the individual level. We review here the experiments currently realized in our laboratory, concerning the use of single NV color center as single photon source and the coherent magnetic manipulation of the electron spin associated to a single NV color center. Furthermore, we demonstrate a nanoscopy experiment based on saturation absorption effect, which allows to optically pin-point single NV color center at a sub-? resolution. This opens a possibility to independently address two or multiple magnetically-coupled single NV color centers, which is a necessary step toward the realization of a diamond-based quantum computer.Comment: 8 page

A Structural Balance Sheet Model of Sovereign Credit Risk

This article studies sovereign credit spreads using a contingent claims model and a balance sheet representation of the sovereign economy. Analytical formulae for domestic and external debt values as well as for the financial guarantee are derived in a framework where recovery rate is endogenously determined as the solution of a strategic bargaining game. The approach allows to relate sovereign credit spreads to observable macroeconomic factors, and in particular accounts for contagion effects through the corporate and banking sectors. Pricing performance as well as predictions about credit spread determinants are successfully tested on the Brazilian economy.Sovereign credit spread, Balance sheet, Recovery rate, Contingent claims analysis, Contagion effects

Controlling single diamond NV color center photoluminescence spectrum with a Fabry-Perot microcavity

We present both theoretical and experimental results on fluorescence of single defect centers in diamond nanocrystals embedded in a planar dielectric microcavity. From a theoretical point of view, we show that the overall fluorescence collection efficiency using moderate numerical aperture microscope objective can be enhanced by using a low quality factor microcavity. This could be used in particular for low temperature applications where the numerical aperture of collection microscope objectives is limited due to the experimental constraints. We experimentally investigate the control of the fluorescence spectrum of the emitted light from a single center. We show the simultaneous narrowing of the room temperature broadband emission spectrum and the increase of the fluorescence spectral density.Comment: 22 pages, 10 figure

Déterminants de la participation à une plateforme collaborative

Comprend des références bibliographiquesLe projet pilote de site de collaboration mis de l’avant pour les cohortes inscrites au programme de deuxième cycle en gestion de la formation se veut une façon de permettre aux apprenants d’expérimenter cette formule en mode « incubateur ». Il vise à accroître la flexibilité de l’offre de formation, à assurer une continuité dans l’expérience pédagogique et à favoriser la réutilisation d’un tel outil en milieu organisationnel. Après avoir décrit la problématique de départ, nous présentons différentes recherches qui nous ont servi de guide dans l’élaboration de cette pratique innovante. Afin de tirer profit de ces recherches portant sur les communautés de pratique virtuelles, nous avons d’abord mis en place un projet pilote en vue d’effectuer une analyse en tenant compte des de l’animation comme variable déterminante de la participation et du succès

Narrow-band single-photon emission in the near infrared for quantum key distribution

We report on the observation of single colour centers in natural diamond samples emitting in the near infrared region when optically excited. Photoluminescence of these single emitters have several striking features, such as a narrow-band fully polarized emission (FWHM 2 nm) around 780 nm, a short excited-state lifetime of about 2 ns, and perfect photostability at room temperature under our excitation conditions. We present a detailed study of their photophysical properties. Development of a triggered single-photon source relying on this single colour centre is discussed in the prospect of its application to quantum key distribution.Comment: 9 page

Superconducting quantum node for entanglement and storage of microwave radiation

Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the timed-controlled generation of an entangled state distributed between the node and a microwave channel.Comment: 6 pages, 4 figures. Supplementary information can be downloaded as the ancillary file her

Influence of a static magnetic field on the photoluminescence of an ensemble of Nitrogen-Vacancy color centers in a diamond single-crystal

We investigate the electron spin resonance of an ensemble of Nitrogen-Vacancy (NV) color centers in a bulk diamond crystal. The four possible orientations of the NV-center in the lattice lead to different dependences on the magnitude and the orientation of an external static magnetic field. Experimental results obtained with a continuous microwave excitation are in good agreement with simulations. In addition, we observe that the average radiative lifetime of the NV color center is also modified when the external magnetic field is applied. This variation is explained by the mixing between mS = 0 and mS = $\pm$1 spin states of the NV-center with different radiative lifetimes, due to magnetic coupling. These results are of interest for a broad range of applications, such as spin-resonance-based magnetometry with a high-density ensemble of NV-centersComment: 14 pages, published on Applied Physics Letters journa

Experimental realization of Wheeler's delayed-choice GedankenExperiment

The quantum "mystery which cannot go away" (in Feynman's words) of wave-particle duality is illustrated in a striking way by Wheeler's delayed-choice GedankenExperiment. In this experiment, the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it : either the interferometer is \textit{closed} (\textit{i.e.} the two paths are recombined) and the interference is observed, or the interferometer remains \textit{open} and the path followed by the photon is measured. We report an almost ideal realization of that GedankenExperiment, where the light pulses are true single photons, allowing unambiguous which-way measurements, and the interferometer, which has two spatially separated paths, produces high visibility interference. The choice between measuring either the 'open' or 'closed' configuration is made by a quantum random number generator, and is space-like separated -- in the relativistic sense -- from the entering of the photon into the interferometer. Measurements in the closed configuration show interference with a visibility of 94%, while measurements in the open configuration allow us to determine the followed path with an error probability lower than 1%

Wheeler's delayed-choice thought experiment: Experimental realization and theoretical analysis

Wheeler has strikingly illustrated the wave-particle duality by the delayed-choice thought experiment, in which the configuration of a 2-path interferometer is chosen after a single-photon light-pulsed has entered it. We present a quantitative theoretical analysis of an experimental realization of Wheeler's proposal

An optimization dichotomy for capital injections and absolutely continuous dividend strategies

We consider an optimal stochastic control problem in which a firm's cash/surplus process is controlled by dividend payments and capital injections. Stockholders aim to maximize their dividend stream minus the cost of injecting capital, if needed. We consider absolutely continuous dividend policies subject to a level-dependent upper bound on the dividend rate while we allow for general capital injections behavior. We prove that the optimal strategy can only be of two types: dividends are paid according to a \textit{mean-reverting} strategy with capital injections performed each time the cash process reaches zero; or, dividends are paid according to another \textit{mean-reverting} strategy and no injection of capital is ever made, until ruin is reached. We give a complete solution to this problem and characterize this dichotomy by comparing (the derivatives of) the value functions at zero of two sub-problems. The first sub-problem is concerned solely with the maximization of dividends, while the second sub-problem is the corresponding bail-out optimal dividend problem for which we provide also a complete solution