85 research outputs found
Observation of Feshbach resonances in an ultracold gas of Cr
We have observed Feshbach resonances in elastic collisions between ultracold
Cr atoms. This is the first observation of collisional Feshbach
resonances in an atomic species with more than one valence electron. The zero
nuclear spin of Cr and thus the absence of a Fermi-contact interaction
leads to regularly-spaced resonance sequences. By comparing resonance positions
with multi-channel scattering calculations we determine the s-wave scattering
length of the lowest potentials to be
\unit[112(14)]{a_0}, \unit[58(6)]{a_0} and -\unit[7(20)]{a_0} for S=6, 4,
and 2, respectively, where a_{0}=\unit[0.0529]{nm}.Comment: 4 pages, 2 figures, 1 tabl
Laser cooling of a magnetically guided ultra cold atom beam
We report on the transverse laser cooling of a magnetically guided beam of
ultra cold chromium atoms. Radial compression by a tapering of the guide is
employed to adiabatically heat the beam. Inside the tapered section heat is
extracted from the atom beam by a two-dimensional optical molasses
perpendicular to it, resulting in a significant increase of atomic phase space
density. A magnetic offset field is applied to prevent optical pumping to
untrapped states. Our results demonstrate that by a suitable choice of the
magnetic offset field, the cooling beam intensity and detuning, atom losses and
longitudinal heating can be avoided. Final temperatures below 65 microkelvin
have been achieved, corresponding to an increase of phase space density in the
guided beam by more than a factor of 30.Comment: 9 pages, 4 figure
The effect of light assisted collisions on matter wave coherence in superradiant Bose-Einstein condensates
We investigate experimentally the effects of light assisted collisions on the
coherence between momentum states in Bose-Einstein condensates. The onset of
superradiant Rayleigh scattering serves as a sensitive monitor for matter wave
coherence. A subtle interplay of binary and collective effects leads to a
profound asymmetry between the two sides of the atomic resonance and provides
far bigger coherence loss rates for a condensate bathed in blue detuned light
than previously estimated. We present a simplified quantitative model
containing the essential physics to explain our experimental data and point at
a new experimental route to study strongly coupled light matter systems.Comment: 10 pages, 4 figure
Collective Electronic Excitation Coupling between Planar Optical Lattices using Ewald's Method
Using Ewald's summation method we investigate collective electronic
excitations (excitons) of ultracold atoms in parallel planar optical lattices
including long range interactions. The exciton dispersion relation can then be
suitably rewritten and efficiently calculated for long range resonance
dipole-dipole interactions. Such in-plane excitons resonantly couple for two
identical optical lattices, with an energy transfer strength decreasing
exponentially with the distance between the lattices. This allows a restriction
of the transfer to neighboring planes and gives rise to excitons delocalized
between the lattices. In general equivalent results will hold for any planar
system containing lattice layers of optically active and dipolar materials.Comment: 6 pages, and 7 figure
Optimized loading of an optical dipole trap for the production of Chromium BECs
We report on a strategy to maximize the number of chromium atoms transferred
from a magneto-optical trap into an optical trap through accumulation in
metastable states via strong optical pumping. We analyse how the number of
atoms in a chromium Bose Einstein condensate can be raised by a proper handling
of the metastable state populations. Four laser diodes have been implemented to
address the four levels that are populated during the MOT phase. The individual
importance of each state is specified. To stabilize two of our laser diode, we
have developed a simple ultrastable passive reference cavity whose long term
stability is better than 1 MHz
Radiating and non-radiating sources in elasticity
In this work, we study the inverse source problem of a fixed frequency for
the Navier's equation. We investigate that nonradiating external forces. If the
support of such a force has a convex or non-convex corner or edge on their
boundary, the force must be vanishing there. The vanishing property at corners
and edges holds also for sufficiently smooth transmission eigenfunctions in
elasticity. The idea originates from the enclosure method: The energy identity
and new type exponential solutions for the Navier's equation.Comment: 17 page
Effect of Quadratic Zeeman Energy on the Vortex of Spinor Bose-Einstein Condensates
The spinor Bose-Einstein condensate of atomic gases has been experimentally
realized by a number of groups. Further, theoretical proposals of the possible
vortex states have been sugessted. This paper studies the effects of the
quadratic Zeeman energy on the vortex states. This energy was ignored in
previous theoretical studies, although it exists in experimental systems. We
present phase diagrams of various vortex states taking into account the
quadratic Zeeman energy. The vortex states are calculated by the
Gross-Pitaevskii equations. Several new kinds of vortex states are found. It is
also found that the quadratic Zeeman energy affects the direction of total
magnetization and causes a significant change in the phase diagrams.Comment: 6 pages, 5 figures. Published in J. Phys. Soc. Jp
Free Expansion of a Weakly-interacting Dipolar Fermi Gas
We theoretically investigate a polarized dipolar Fermi gas in free expansion.
The inter-particle dipolar interaction deforms phase-space distribution in trap
and also in the expansion. We exactly predict the minimal quadrupole
deformation in the expansion for the high-temperature Maxwell-Boltzmann and
zero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov
approaches. In conclusion, we provide a proper approach to develop the
time-of-flight method for the weakly-interacting dipolar Fermi gas and also
reveal a scaling law associated with the Liouville's theorem in the long-time
behaviors of the both gases
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