1,073 research outputs found
Effect of thermal fluctuations on spin degrees of freedom in spinor Bose-Einstein condensates
We consider the effect of thermal fluctuations on rotating spinor F=1
condensates in axially-symmetric vortex phases, when all the three hyperfine
states are populated. We show that the relative phase among different
components of the order parameter can fluctuate strongly due to the weakness of
the interaction in the spin channel. These fluctuations can be significant even
at low temperatures. Fluctuations of relative phase lead to significant
fluctuations of the local transverse magnetization of the condensate. We
demonstrate that these fluctuations are much more pronounced for the
antiferromagnetic state than for the ferromagnetic one.Comment: 5 pages, 2 figures; final version, accepted for publication in Phys.
Rev.
Performance limitations of subband adaptive filters
In this paper, we evaluate the performance limitations of subband adaptive filters in terms of achievable final error terms. The limiting factors are the aliasing level in the subbands, which poses a distortion and thus presents a lower bound for the minimum mean squared error in each subband, and the distortion function of the overall filter bank, which in a system identification setup restricts the accuracy of the equivalent fullband model. Using a generalized DFT modulated filter bank for the subband decomposition, both errors can be stated in terms of the underlying prototype filter. If a source model for coloured input signals is available, it is also possible to calculate the power spectral densities in both subbands and reconstructed fullband. The predicted limits of error quantities compare favourably with simulations presented
Prospect of creating a composite fermi/bose superfluid
We show that composite fermi/bose superfluids can be created in cold-atom
traps by employing a Feshbach resonance or coherent photoassociation. The
bosonic molecular condensate created in this way implies a new fermion pairing
mechanism associated with the exchange of fermion pairs between the molecular
condensate and an atomic fermion superfluid. We predict macroscopically
coherent, Josephson-like oscillations of the atomic and molecular populations
in response to a sudden change of the molecular energy, and suggest that these
oscillations will provide an experimental signature of the pairing.Comment: Rejected by PR
Vortex structure in spinor F=2 Bose-Einstein condensates
Extended Gross-Pitaevskii equations for the rotating F=2 condensate in a
harmonic trap are solved both numerically and variationally using trial
functions for each component of the wave function. Axially-symmetric vortex
solutions are analyzed and energies of polar and cyclic states are calculated.
The equilibrium transitions between different phases with changing of the
magnetization are studied. We show that at high magnetization the ground state
of the system is determined by interaction in "density" channel, and at low
magnetization spin interactions play a dominant role. Although there are five
hyperfine states, all the particles are always condensed in one, two or three
states. Two novel types of vortex structures are also discussed.Comment: 6 pages, 3 figure
Nanoplasmonics beyond Ohm's law
In tiny metallic nanostructures, quantum confinement and nonlocal response
change the collective plasmonic behavior with important consequences for e.g.
field-enhancement and extinction cross sections. We report on our most recent
developments of a real-space formulation of an equation-of-motion that goes
beyond the common local-response approximation and use of Ohm's law as the
central constitutive equation. The electron gas is treated within a
semi-classical hydrodynamic model with the emergence of a new intrinsic length
scale. We briefly review the new governing wave equations and give examples of
applying the nonlocal framework to calculation of extinction cross sections and
field enhancement in isolated particles, dimers, and corrugated surfaces.Comment: Invited paper for TaCoNa-Photonics 2012 (www.tacona-photonics.org),
to appear in AIP Conf. Pro
Photosynthetic characteristics of the benthic diatom species Nitzschia frustulum (KĂĽtzing) Grunow isolated from a soda pan along temperature-, sulfate- and chloride gradients
Variational collocation on finite intervals
In this paper we study a new family of sinc--like functions, defined on an
interval of finite width. These functions, which we call ``little sinc'', are
orthogonal and share many of the properties of the sinc functions. We show that
the little sinc functions supplemented with a variational approach enable one
to obtain accurate results for a variety of problems. We apply them to the
interpolation of functions on finite domain and to the solution of the
Schr\"odinger equation, and compare the performance of present approach with
others.Comment: 12 pages, 8 figures, 1 tabl
A laser-driven target of high-density nuclear polarized hydrogen gas
We report the best figure-of-merit achieved for an internal nuclear polarized
hydrogen gas target and a Monte Carlo simulation of spin-exchange optical
pumping. The dimensions of the apparatus were optimized using the simulation
and the experimental results were in good agreement with the simulation. The
best result achieved for this target was 50.5% polarization with 58.2% degree
of dissociation of the sample beam exiting the storage cell at a hydrogen flow
rate of atoms/s.Comment: Accepted as a Rapid Communication article in Phys. Rev.
- …