2,022 research outputs found
Superfluid-Mott Insulator Transition of Spin-1 Bosons in an Optical Lattice
We have studied superfluid-Mott insulating transition of spin-1 bosons
interacting antiferromagnetically in an optical lattice. We have obtained the
zero-temperature phase diagram by a mean-field approximation and have found
that the superfluid phase is to be a polar state as a usual trapped spin-1 Bose
gas. More interestingly, we have found that the Mott-insulating phase is
strongly stabilized only when the number of atoms per site is even.Comment: 9 pages, 1 figur
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
Static properties and spin dynamics of the ferromagnetic spin-1 Bose gas in magnetic field
Properties of spin-1 Bose gases with ferromagnetic interaction in the
presence of a nonzero magnetic field are studied. The equation of state and
thermodynamic quantities are worked out with the help of a mean-field
approximation. The phase diagram besides Bose-Einstein condensation contains a
first order transition where two values of the magnetization coexist. The
dynamics is investigated with the help of the Random Phase Approximation. The
soft mode corresponding to the critical point of the magnetic phase transition
is found to behave like in conventional theory.Comment: 8 pages and 3 figures included in text, submitted to Physical Review
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
Bose-Einstein condensation at constant temperature
We present a novel experimental approach to Bose-Einstein condensation by
increasing the particle number of the system at almost constant temperature. In
particular the emergence of a new condensate is observed in multi-component F=1
spinor condensates of 87-Rb. Furthermore we develop a simple rate-equation
model for multi-component BEC thermodynamics at finite temperature which well
reproduces the measured effects.Comment: 4 pages, 3 figures, RevTe
Ultra-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
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