7,629 research outputs found
Decoherence-driven Cooling of a Degenerate Spinor Bose Gas
We investigate the relationship between the coherence of a partially
Bose-condensed spinor gas and its temperature. We observe cooling of the normal
component driven by decoherence as well the effect of temperature on
decoherence rates.Comment: 4 pages, 2 figure
The Mystery of the Ramsey Fringe that Didn't Chirp
We use precision microwave spectroscopy of magnetically trapped, ultra-cold
87Rb to characterize intra- and inter-state density correlations. The cold
collision shifts for both normal and condensed clouds are measured. The results
verify the presence of the sometimes controversial "factors of two", in
normal-cloud mean-field energies, both within a particular state and between
two distinct spin species. One might expect that as two spin species decohere,
the inter-state factor of two would revert to unity, but the associated
frequency chirp one naively expects from such a trend is not observed in our
data.Comment: Proceedings of the 18th International Conference on Atomic Physics
(ICAP 2002
Refined Simulations of the Reaction Front for Diffusion-Limited Two-Species Annihilation in One Dimension
Extensive simulations are performed of the diffusion-limited reaction
AB in one dimension, with initially separated reagents. The reaction
rate profile, and the probability distributions of the separation and midpoint
of the nearest-neighbour pair of A and B particles, are all shown to exhibit
dynamic scaling, independently of the presence of fluctuations in the initial
state and of an exclusion principle in the model. The data is consistent with
all lengthscales behaving as as . Evidence of
multiscaling, found by other authors, is discussed in the light of these
findings.Comment: Resubmitted as TeX rather than Postscript file. RevTeX version 3.0,
10 pages with 16 Encapsulated Postscript figures (need epsf). University of
Geneva preprint UGVA/DPT 1994/10-85
The Reaction-Diffusion Front for in One Dimension
We study theoretically and numerically the steady state diffusion controlled
reaction , where currents of and particles
are applied at opposite boundaries. For a reaction rate , and equal
diffusion constants , we find that when the
reaction front is well described by mean field theory. However, for , the front acquires a Gaussian profile - a result of
noise induced wandering of the reaction front center. We make a theoretical
prediction for this profile which is in good agreement with simulation.
Finally, we investigate the intrinsic (non-wandering) front width and find
results consistent with scaling and field theoretic predictions.Comment: 11 pages, revtex, 4 separate PostScript figure
Persistence exponents for fluctuating interfaces
Numerical and analytic results for the exponent \theta describing the decay
of the first return probability of an interface to its initial height are
obtained for a large class of linear Langevin equations. The models are
parametrized by the dynamic roughness exponent \beta, with 0 < \beta < 1; for
\beta = 1/2 the time evolution is Markovian. Using simulations of
solid-on-solid models, of the discretized continuum equations as well as of the
associated zero-dimensional stationary Gaussian process, we address two
problems: The return of an initially flat interface, and the return to an
initial state with fully developed steady state roughness. The two problems are
shown to be governed by different exponents. For the steady state case we point
out the equivalence to fractional Brownian motion, which has a return exponent
\theta_S = 1 - \beta. The exponent \theta_0 for the flat initial condition
appears to be nontrivial. We prove that \theta_0 \to \infty for \beta \to 0,
\theta_0 \geq \theta_S for \beta
1/2, and calculate \theta_{0,S} perturbatively to first order in an expansion
around the Markovian case \beta = 1/2. Using the exact result \theta_S = 1 -
\beta, accurate upper and lower bounds on \theta_0 can be derived which show,
in particular, that \theta_0 \geq (1 - \beta)^2/\beta for small \beta.Comment: 12 pages, REVTEX, 6 Postscript figures, needs multicol.sty and
epsf.st
Normal-superfluid interaction dynamics in a spinor Bose gas
Coherent behavior of spinor Bose-Einstein condensates is studied in the
presence of a significant uncondensed (normal) component. Normal-superfluid
exchange scattering leads to a near-perfect local alignment between the spin
fields of the two components. Through this spin locking, spin-domain formation
in the condensate is vastly accelerated as the spin populations in the
condensate are entrained by large-amplitude spin waves in the normal component.
We present data evincing the normal-superfluid spin dynamics in this regime of
complicated interdependent behavior.Comment: 5 pages, 4 fig
Analysis of the decay
In this paper we study the angular distribution of the rare B decay , which is expected to be observed soon. We use the
standard effective Hamiltonian approach, and use the form factors that have
already been estimated for the corresponding radiative decay . The additional form factors that come into play for the dileptonic
channel are estimated using the large energy effective theory (LEET), which
enables one to relate the additional form factors to the form factors for the
radiative mode. Our results provide, just like in the case of the
resonance, an opportunity for a straightforward comparison of the basic theory
with experimental results which may be expected in the near future for this
channel.Comment: 14 pages, 5 figures; as accepted for Phys. Rev.
Quasi-normal modes for doubly rotating black holes
Based on the work of Chen, L\"u and Pope, we derive expressions for the
dimensional metric for Kerr-(A)dS black holes with two independent
rotation parameters and all others set equal to zero: . The Klein-Gordon equation is then explicitly separated on this
background. For this separation results in a radial equation coupled
to two generalized spheroidal angular equations. We then develop a full
numerical approach that utilizes the Asymptotic Iteration Method (AIM) to find
radial Quasi-Normal Modes (QNMs) of doubly rotating flat Myers-Perry black
holes for slow rotations. We also develop perturbative expansions for the
angular quantum numbers in powers of the rotation parameters up to second
order.Comment: RevTeX 4-1, various figure
Magnetocrystalline anisotropic effect in GdCoFeAsO ()
From a systematic study of the electrical resistivity , magnetic
susceptibility , isothermal magnetization and the specific
heat , a temperature-magnetic field (-) phase diagram has been
established for GdCoFeAsO ( and ) polycrystalline
compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic
(FM) transition of Co electrons () and
antiferromagnetic (AFM) transition of Gd electrons
(). For the Fe-doped sample (), an extra
magnetic reorientation transition takes place below ,
which is likely associated with Co moments. The two magnetic species of Gd and
Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM)
behavior in the magnetic susceptibility. Upon decreasing the temperature (), the magnetocrystalline anisotropy breaks up the FM
order of Co by aligning the moments with the local easy axes of the various
grains, leading to a spin reorientation transition at
. By applying a magnetic field,
monotonically decreases to lower temperatures, while
the is relatively robust against the external field.
On the other hand, the applied magnetic field pulls the magnetization of grains
from the local easy direction to the field direction via a first-order
reorientation transition, with the transition field () increasing
upon cooling the temperature.Comment: accepted by physical Review B 6 figures and 7 page
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