149 research outputs found
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 1: Classical operation
We describe theoretically the main characteristics of the steady state regime
of a type II Optical Parametric Oscillator (OPO) containing a birefringent
plate. In such a device the signal and idler waves are at the same time
linearly coupled by the plate and nonlinearly coupled by the
crystal. This mixed coupling allows, in some well-defined range of the control
parameters, a frequency degenerate operation as well as phase locking between
the signal and idler modes. We describe here a complete model taking into
account all possible effects in the system, \emph{i.e.} arbitrary rotation of
the waveplate, non perfect phase matching, ring and linear cavities. This model
is able to explain the detailed features of the experiments performed with this
system.Comment: To be published in EPJ
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
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
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
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 2 : bright entangled beams generation
We describe theoretically the quantum properties of atype-II Optical
Parametric Oscillator containing a birefringent plate which induces a linear
coupling between the orthogonally polarized signal and idler beams and results
in phase locking between these two beams. As in a classical OPO, the signal and
idler waves show large quantum correlations which can be measured
experimentally due to the phase locking between the two beams. We study the
influence of the waveplate on the various criteria characterizing quantum
correlations. We show in particular that the quantum correlations can be
maximized by using optimized quadratures.Comment: to be published in Eur. Phys. J.
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
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
Generation of two-color polarization-entangled optical beams with a self-phase-locked two-crystal Optical Parametric Oscillator
A new device to generate polarization-entangled light in the continuous
variable regime is introduced. It consists of an Optical Parametric Oscillator
with two type-II phase-matched non-linear crystals orthogonally oriented,
associated with birefringent elements for adjustable linear coupling. We give
in this paper a theoretical study of its classical and quantum properties. It
is shown that two optical beams with adjustable frequencies and well-defined
polarization can be emitted. The Stokes parameters of the two beams are
entangled. The principal advantage of this setup is the possibility to directly
generate polarization entangled light without the need of mixing four modes on
beam splitters as required in current experimental setups. This device opens
new directions for the study of light-matter interfaces and generation of
multimode non-classical light and higher dimensional phase space
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