1,088 research outputs found
Breathing Modes and Hidden Symmetry of Trapped Atoms in 2D
Atoms confined in a harmonic potential show universal oscillations in 2D. We
point out the connection of these ''breathing'' modes to the presence of a
hidden symmetry. The underlying symmetry SO(2,1), i.e. the two dimensional
Lorentz group, allows pulsating solutions to be constructed for the interacting
quantum system and for the corresponding nonlinear Gross-Pitaevskii equation.
We point out how this symmetry can be used as a probe for recently proposed
experiments of trapped atoms in 2D.Comment: 4 pages, small changes in title and text, references adde
Influence of seating styles on head and pelvic vertical movement symmetry in horses ridden at trot
Detailed knowledge of how a rider’s seating style and riding on a circle influences the movement symmetry of the horse’s head and pelvis may aid rider and trainer in an early recognition of low grade lameness. Such knowledge is also important during both subjective and objective lameness evaluations in the ridden horse in a clinical setting. In this study, inertial sensors were used to assess how different rider seating styles may influence head and pelvic movement symmetry in horses trotting in a straight line and on the circle in both directions. A total of 26 horses were subjected to 15 different conditions at trot: three unridden conditions and 12 ridden conditions where the rider performed three different seating styles (rising trot, sitting trot and two point seat). Rising trot induced systematic changes in movement symmetry of the horses. The most prominent effect was decreased pelvic rise that occurred as the rider was actively rising up in the stirrups, thus creating a downward momentum counteracting the horses push off. This mimics a push off lameness in the hindlimb that is in stance when the rider sits down in the saddle during the rising trot. On the circle, the asymmetries induced by rising trot on the correct diagonal counteracted the circle induced asymmetries, rendering the horse more symmetrical. This finding offers an explanation to the equestrian tradition of rising on the ‘correct diagonal.’ In horses with small pre-existing movement asymmetries, the asymmetry induced by rising trot, as well as the circular track, attenuated or reduced the horse’s baseline asymmetry, depending on the sitting diagonal and direction on the circle. A push off hindlimb lameness would be expected to increase when the rider sits during the lame hindlimb stance whereas an impact hindlimb lameness would be expected to decrease. These findings suggest that the rising trot may be useful for identifying the type of lameness during subjective lameness assessment of hindlimb lameness. This theory needs to be studied further in clinically lame horses
Quantum critical behavior in strongly interacting Rydberg gases
We study the appearance of correlated many-body phenomena in an ensemble of
atoms driven resonantly into a strongly interacting Rydberg state. The ground
state of the Hamiltonian describing the driven system exhibits a second order
quantum phase transition. We derive the critical theory for the quantum phase
transition and show that it describes the properties of the driven Rydberg
system in the saturated regime. We find that the suppression of Rydberg
excitations known as blockade phenomena exhibits an algebraic scaling law with
a universal exponent.Comment: 4 pages, 3 figures, published versio
Expansion dynamics of a dipolar Bose-Einstein condensate
Our recent measurements on the expansion of a chromium dipolar condensate
after release from an optical trapping potential are in good agreement with an
exact solution of the hydrodynamic equations for dipolar Bose gases. We report
here the theoretical method used to interpret the measurement data as well as
more details of the experiment and its analysis. The theory reported here is a
tool for the investigation of different dynamical situations in time-dependent
harmonic traps.Comment: 12 pages. Submitted to PR
Stable periodic density waves in dipolar Bose-Einstein condensates trapped in optical lattices
Density-wave patterns in (quasi-) discrete media with local interactions are
known to be unstable. We demonstrate that \emph{stable} double- and triple-
period patterns (DPPs and TPPs), with respect to the period of the underlying
lattice, exist in media with nonlocal nonlinearity. This is shown in detail for
dipolar Bose-Einstein condensates (BECs), loaded into a deep one-dimensional
(1D) optical lattice (OL), by means of analytical and numerical methods in the
tight-binding limit. The patterns featuring multiple periodicities are
generated by the modulational instability of the continuous-wave (CW) state,
whose period is identical to that of the OL. The DPP and TPP emerge via phase
transitions of the second and first kind, respectively. The emerging patterns
may be stable provided that the dipole-dipole (DD) interactions are repulsive
and sufficiently strong, in comparison with the local repulsive nonlinearity.
Within the set of the considered states, the TPPs realize a minimum of the free
energy. Accordingly, a vast stability region for the TPPs is found in the
parameter space, while the DPP\ stability region is relatively narrow. The same
mechanism may create stable density-wave patterns in other physical media
featuring nonlocal interactions, such as arrayed optical waveguides with
thermal nonlinearity.Comment: 7 pages, 4 figures, Phys. Rev. Lett., in pres
Bose-Einstein condensation of chromium
We report on the generation of a Bose-Einstein condensate in a gas of
chromium atoms, which will make studies of the effects of anisotropic
long-range interactions in degenerate quantum gases possible. The preparation
of the chromium condensate requires novel cooling strategies that are adapted
to its special electronic and magnetic properties. The final step to reach
quantum degeneracy is forced evaporative cooling of 52Cr atoms within a crossed
optical dipole trap. At a critical temperature of T~700nK, we observe
Bose-Einstein condensation by the appearance of a two-component velocity
distribution. Released from an anisotropic trap, the condensate expands with an
inversion of the aspect ratio. We observe critical behavior of the condensate
fraction as a function of temperature and more than 50,000 condensed 52Cr
atoms.Comment: 4 pages, 4 figure
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