273 research outputs found
Bose-Einstein condensation of metastable helium: some experimental aspects
We describe our recent realization of BEC using metastable helium. All
detection is done with a micruchannel plate which detects the metastables or
ions coming from the trapped atom cloud. This discussion emphasizes some of the
diagnostic experiments which were necessary to quantitatively analyse our
results.Comment: 5 pages, 3 figure
Bose-Einstein Condensation and Spin Mixtures of Optically Trapped Metastable Helium
We report the realization of a BEC of metastable helium-4 atoms (4He*) in an
all optical potential. Up to 10^5 spin polarized 4He* atoms are condensed in an
optical dipole trap formed from a single, focused, vertically propagating far
off-resonance laser beam. The vertical trap geometry is chosen to best match
the resolution characteristics of a delay-line anode micro-channel plate
detector capable of registering single He* atoms. We also confirm the
instability of certain spin state combinations of 4He* to two-body inelastic
processes, which necessarily affects the scope of future experiments using
optically trapped spin mixtures. In order to better quantify this constraint,
we measure spin state resolved two-body inelastic loss rate coefficients in the
optical trap
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
Hanbury Brown and Twiss correlations in atoms scattered from colliding condensates
Low energy elastic scattering between clouds of Bose condensed atoms leads to
the well known s-wave halo with atoms emerging in all directions from the
collision zone. In this paper we discuss the emergence of Hanbury Brown and
Twiss coincidences between atoms scattered in nearly parallel directions. We
develop a simple model that explains the observations in terms of an
interference involving two pairs of atoms each associated with the elementary s
wave scattering process.Comment: Minor corrections. reference update
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
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
Ionization rates in a Bose-Einstein condensate of metastable Helium
We have studied ionizing collisions in a BEC of He*. Measurements of the ion
production rate combined with measurements of the density and number of atoms
for the same sample allow us to estimate both the 2 and 3-body contributions to
this rate. A comparison with the decay of the number of condensed atoms in our
magnetic trap, in the presence of an rf-shield, indicates that ionizing
collisions are largely or wholly responsible for the loss. Quantum depletion
makes a substantial correction to the 3-body rate constant.Comment: 4 pages, 3 figure
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