25 research outputs found
Breakdown of scale invariance in a quasi-two-dimensional Bose gas due to the presence of the third dimension
In this Rapid Communication, we describe how the presence of the third
dimension may break the scale invariance in a two-dimensional Bose gas in a
pancake-shaped trap. From the two-dimensional perspective, the possibility of a
weak spilling of the atomic density beyond the ground-state of the confinement
alters the two-dimensional chemical potential; in turn, this correction no
longer supports scale invariance. We compare experimental data with numerical
and analytic perturbative results and find a good agreement.Comment: 4 pages, 1 figure, published in PRA Rapid Com
Imaging the collective excitations of an ultracold gas using statistical correlations
Advanced data analysis techniques have proved to be crucial for extracting
information from noisy images. Here we show that principal component analysis
can be successfully applied to ultracold gases to unveil their collective
excitations. By analyzing the correlations in a series of images we are able to
identify the collective modes which are excited, determine their population,
image their eigenfunction, and measure their frequency. Our method allows to
discriminate the relevant modes from other noise components and is robust with
respect to the data sampling procedure. It can be extended to other dynamical
systems including cavity polariton quantum gases or trapped ions.Comment: See also the supplementary material and the video abstrac
Experimental investigation of amplitude and phase quantum correlations in a type II OPO above threshold: from the non-degenerate to the degenerate operation
We describe a very stable type II optical parametric oscillator operated
above threshold which provides 9.7 0.5 dB (89%) of quantum noise
reduction on the intensity difference of the signal and idler modes. We also
report the first experimental study by homodyne detection of the generated
bright two-mode state in the case of frequency degenerate operation obtained by
introducing a birefringent plate inside the optical cavity
Probing superfluidity in a quasi two-dimensional Bose gas through its local dynamics
We report direct evidence of superfluidity in a quasi two-dimensional Bose
gas by observing its dynamical response to a collective excitation. Relying on
a novel local correlation analysis, we are able to probe inhomogeneous clouds
and reveal their local dynamics. We identify in this way the superfluid and
thermal phases inside the gas and locate the boundary at which the
Berezinskii--Kosterlitz--Thouless crossover occurs. This new analysis also
allows to evidence the coupling of the two fluids which induces at finite
temperatures damping rates larger than the usual Landau damping
Experimental evidence of spontaneous symmetry breaking in intracavity type-II second harmonic generation with triple resonance
We describe an experiment showing a spontaneous symmetry breaking phenomenon
between the intensities of the ordinary and extraordinary components of the
fundamental field in intracavity type-II harmonic generation. It is based on a
triply resonant dual cavity containing a type II phase matched
crystal pumped at the fundamental frequency . The pump beam generates
in the cavity a second harmonic mode at frequency which acts as a
pump for frequency degenerate type II parametric down conversion. Under
operating conditions which are precisely symmetric with respect to the ordinary
and extraordinary components of the fundamental wave, we have observed a
breaking of the symmetry on the intensities of these two waves in agreement
with the theoretical predictions.Comment: submitte
Source laser intense pour le refroidissement du 87Rb par doublement de fréquence d'un laser fibré télécom
to appear in EPJ-ST; COLOQ11 ProceedingsWe built a frequency-doubled laser for 87Rb laser cooling, from a Telecom fiber laser. Thanks to intense technological development, telecom fiber lasers exhibit outstanding properties regarding relative intensity noise and modulation bandwidth. The enhanced doubling efficiency of periodically poled crystals allowed to obtain up to 1.8 W at 780 nm from 10 W at 1560 nm, with a simple pass configuration in a 50-mm long crystal of ppLN:MgO. This technique can also be applied at the wavelength of potassium (767 nm) (Bourdel, 2009) and could be of great interest for the realization of dipole traps
Influence of the Radio-Frequency source properties on RF-based atom traps
We discuss the quality required for the RF source used to trap neutral atoms
in RF-dressed potentials. We illustrate this discussion with experimental
results obtained on a Bose-Einstein condensation experiment with different RF
sources.Comment: 5 figures, 7 page
Effets de polarisation dans les mélanges paramétriques à trois ondes en cavité : applications au traitement classique et quantique de l'information
We study in detail polarization effects in intracavity three-wave mixing. We first focus on a theoretical study of a type II Optical Parametric Oscillator (OPO) in which we put a birefringent plate. In a type II crystal, signal and idler are orthogonally polarized and we show that the plate-induced coupling creates a locking zone where the OPO operates at frequency degeneracy. After a further development of the classical properties of the system we study the quantum entanglement of the twin beams and connect the results with various quantum information criteria. We also study, both experimentally and theoretically, an all-optical regeneration scheme based on type II parametric cascading with dual-cavity and examine the feasability of this system in the telecom range.Nous étudions en détail les effets de polarisation dans les mélanges paramétriques à trois ondes en cavité. Nous nous intéressons tout d'abord à l'étude théorique de l'Oscillateur Paramétrique Optique (OPO) de type II dans lequel nous insérons une lame biréfringente. En type II signal et complémentaire sont polarisés orthogonalement et nous montrons que le couplage induit par la lame créée une zone d'accrochage où l'OPO fonctionne à dégénérescence de fréquence. Après avoir caractérisé de manière approfondie les propriétés classiques de ce système, nous étudions l'intrication quantique des faisceaux jumeaux et relions les résultats obtenus à différents critères d'information quantique. Nous faisons également l'étude expérimentale et théorique d'un système de régénération tout-optique basé sur la génération vectorielle de seconde harmonique à reconversion paramétrique de type II avec une double cavité et étudions la faisabilité d'un tel système dans des conditions télécom
Effets de polarisation dans les mélanges paramétriques à trois ondes en cavité (applications au traitement classique et quantique de l'information)
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF