277 research outputs found
Thermal counting statistics in an atomic two-mode squeezed vacuum state
We measure the population distribution in one of the atomic twin beams
generated by four-wave mixing in an optical lattice.
Although the produced two-mode squeezed vacuum state is pure, each individual
mode is described as a statistical mixture.
We confirm the prediction that the particle number follows an exponential
distribution when only one spatio-temporal mode is selected.
We also show that this distribution accounts well for the contrast of an
atomic Hong--Ou--Mandel experiment.
These experiments constitute an important validation of our twin beam source
in view of a future test of a Bell inequalities.Comment: SciPost submissio
Hanbury Brown Twiss effect for ultracold quantum gases
We have studied 2-body correlations of atoms in an expanding cloud above and
below the Bose-Einstein condensation threshold. The observed correlation
function for a thermal cloud shows a bunching behavior, while the correlation
is flat for a coherent sample. These quantum correlations are the atomic
analogue of the Hanbury Brown Twiss effect. We observe the effect in three
dimensions and study its dependence on cloud size.Comment: Figure 1 availabl
Prediction of intervertebral disc mechanical response to axial load using isotropic and fiber reinforced FE models
International audienc
Getting the elastic scattering length by observing inelastic collisions in ultracold metastable helium atoms
We report an experiment measuring simultaneously the temperatureand the flux
of ions produced by a cloud of triplet metastablehelium atoms at the
Bose-Einstein critical temperature. The onsetof condensation is revealed by a
sharp increase of the ion fluxduring evaporative cooling. Combining our
measurements withprevious measurements of ionization in a pure BEC,we extract
an improved value of the scattering length nm. The analysis
includes corrections takinginto accountthe effect of atomic interactions on the
criticaltemperature, and thus an independent measurement of the
scatteringlength would allow a new test of these calculations
Observation of atom pairs in spontaneous four wave mixing of two colliding Bose-Einstein Condensates
We study atom scattering from two colliding Bose-Einstein condensates using a
position sensitive, time resolved, single atom detector. In analogy to quantum
optics, the process can also be thought of as spontaneous, degenerate four wave
mixing of de Broglie waves. We find a clear correlation between atoms with
opposite momenta, demonstrating pair production in the scattering process. We
also observe a Hanbury Brown and Twiss correlation for collinear momenta, which
permits an independent measurement of the size of the pair production source
and thus the size of the spatial mode. The back to back pairs occupy very
nearly two oppositely directed spatial modes, a promising feature for future
quantum optics experiments.Comment: A few typos have been correcte
Pair correlations of scattered atoms from two colliding Bose-Einstein Condensates: Perturbative Approach
We apply an analytical model for anisotropic, colliding Bose-Einstein
condensates in a spontaneous four wave mixing geometry to evaluate the second
order correlation function of the field of scattered atoms. Our approach uses
quantized scattering modes and the equivalent of a classical, undepleted pump
approximation. Results to lowest order in perturbation theory are compared with
a recent experiment and with other theoretical approaches.Comment: 9 pages, 3 figure
Theory for a Hanbury Brown Twiss experiment with a ballistically expanding cloud of cold atoms
We have studied one-body and two-body correlation functions in a
ballistically expanding, non-interacting atomic cloud in the presence of
gravity. We find that the correlation functions are equivalent to those at
thermal equilibrium in the trap with an appropriate rescaling of the
coordinates. We derive simple expressions for the correlation lengths and give
some physical interpretations. Finally a simple model to take into account
finite detector resolution is discussed
Theory of an optical dipole trap for cold atoms
The theory of an atom dipole trap composed of a focused, far red-detuned, trapping laser beam, and a pair of red-detuned, counterpropagating, cooling beams is developed for the simplest realistic multilevel dipole interaction scheme based on a model of a (3+5)-level atom. The description of atomic motion in the trap is based on the quantum kinetic equations for the atomic density matrix and the reduced quasiclassical kinetic equation for atomic distribution function. It is shown that when the detuning of the trapping field is much larger than the detuning of the cooling field, and with low saturation, the one-photon absorption (emission) processes responsible for the trapping potential can be well separated from the two-photon processes responsible for sub-Doppler cooling atoms in the trap. Two conditions are derived that are necessary and sufficient for stable atomic trapping. The conditions show that stable atomic trapping in the optical dipole trap can be achieved when the trapping field has no effect on the two-photon cooling process and when the cooling field does not change the structure of the trapping potential but changes only the numerical value of the trapping potential well. It is concluded that the separation of the trapping and cooling processes in a pure optical dipole trap allows one to cool trapped atoms down to a minimum temperature close to the recoil temperature, keeping simultaneously a deep potential well
State-Insensitive Cooling and Trapping of Single Atoms in an Optical Cavity
Single Cesium atoms are cooled and trapped inside a small optical cavity by
way of a novel far-off-resonance dipole-force trap (FORT), with observed
lifetimes of 2 to 3 seconds. Trapped atoms are observed continuously via
transmission of a strongly coupled probe beam, with individual events lasting ~
1 s. The loss of successive atoms from the trap N = 3 -> 2 -> 1 -> 0 is thereby
monitored in real time. Trapping, cooling, and interactions with strong
coupling are enabled by the FORT potential, for which the center-of-mass motion
is only weakly dependent on the atom's internal state.Comment: 5 pages, 4 figures Revised version to appear in Phys. Rev. Let
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