409 research outputs found
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
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
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
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
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
DĂ©terminants de la participation Ă 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
Balanced homodyne detection in second-harmonic generation microscopy
We demonstrate the association of two-photon nonlinear microscopy with
balanced homodyne detection for investigating second harmonic radiation
properties at nanoscale dimensions. Variation of the relative phase between
second-harmonic and fundamental beams is retrieved, as a function of the
absolute orientation of the nonlinear emitters. Sensitivity down to
approximately 3.2 photon/s in the spatio-temporal mode of the local oscillator
is obtained. This value is high enough to efficiently detect the coherent
second-harmonic emission from a single KTiOPO4 crystal of sub-wavelength size.Comment: 9 pages to appear in Applied Physics Letter
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