235 research outputs found
Multiple imputation for continuous variables using a Bayesian principal component analysis
We propose a multiple imputation method based on principal component analysis
(PCA) to deal with incomplete continuous data. To reflect the uncertainty of
the parameters from one imputation to the next, we use a Bayesian treatment of
the PCA model. Using a simulation study and real data sets, the method is
compared to two classical approaches: multiple imputation based on joint
modelling and on fully conditional modelling. Contrary to the others, the
proposed method can be easily used on data sets where the number of individuals
is less than the number of variables and when the variables are highly
correlated. In addition, it provides unbiased point estimates of quantities of
interest, such as an expectation, a regression coefficient or a correlation
coefficient, with a smaller mean squared error. Furthermore, the widths of the
confidence intervals built for the quantities of interest are often smaller
whilst ensuring a valid coverage.Comment: 16 page
Unconditional quantum cloning of coherent states with linear optics
A scheme for optimal Gaussian cloning of optical coherent states is proposed
and experimentally demonstrated. Its optical realization is based entirely on
simple linear optical elements and homodyne detection. The optimality of the
presented scheme is only limited by detection inefficiencies. Experimentally we
achieved a cloning fidelity of about 65%, which almost touches the optimal
value of 2/3.Comment: Phys. Rev. Lett. Volume 94, Number 24, p. 24050
Measurement of spectral functions of ultracold atoms in disordered potentials
We report on the measurement of the spectral functions of noninteracting
ultracold atoms in a three-dimensional disordered potential resulting from an
optical speckle field. Varying the disorder strength by 2 orders of magnitude,
we observe the crossover from the "quantum" perturbative regime of low disorder
to the "classical" regime at higher disorder strength, and find an excellent
agreement with numerical simulations. The method relies on the use of
state-dependent disorder and the controlled transfer of atoms to create
well-defined energy states. This opens new avenues for experimental
investigations of three-dimensional Anderson localization
Experimental purification of coherent states
We propose a scheme for optimal Gaussian purification of coherent states from
several imperfect copies. The proposal is experimentally demonstrated for the
case of two copies of a coherent state sent through independent noisy channels.
Our purification protocol relies on only linear optics and an ancilla vacuum
state, rendering this approach an interesting alternative to the more complex
protocols of entanglement distillation and quantum error correction
Imputation de données manquantes pour des données mixtes via les méthodes factorielles grùce à missMDA
Imputation de données manquantes pour des données mixtes via les méthodes factorielles grùce à missMD
Efficient polarization squeezing in optical fibers
We report on a novel and efficient source of polarization squeezing using a
single pass through an optical fiber. Simply passing this Kerr squeezed beam
through a carefully aligned lambda/2 waveplate and splitting it on a
polarization beam splitter, we find polarization squeezing of up to 5.1 +/- 0.3
dB. The experimental setup allows for the direct measurement of the squeezing
angle.Comment: 4 pages, 4 figure
Guided Quasicontinuous Atom Laser
We report the first realization of a guided quasicontinuous atom laser by rf
outcoupling a Bose-Einstein condensate from a hybrid optomagnetic trap into a
horizontal atomic waveguide. This configuration allows us to cancel the
acceleration due to gravity and keep the de Broglie wavelength constant at 0.5
m during 0.1 s of propagation. We also show that our configuration,
equivalent to pigtailing an optical fiber to a (photon) semiconductor laser,
ensures an intrinsically good transverse mode matching.Comment: version published in Phys. Rev. Lett. 97, 200402 (2006
Application of lasers to ultracold atoms and molecules
In this review, we discuss the impact of the development of lasers on
ultracold atoms and molecules and their applications. After a brief historical
review of laser cooling and Bose-Einstein condensation, we present important
applications of ultra cold atoms, including time and frequency metrology, atom
interferometry and inertial sensors, atom lasers, simulation of condensed
matter systems, production and study of strongly correlated systems, and
production of ultracold molecules.Comment: Review paper written in the name of IFRAF to celebrate 50 years of
lasers and their applications to cold atom physics; 15 pages, 2 figures; to
appear in Comptes Rendus de l'Academie des Sciences, Pari
- âŠ