2,337 research outputs found
Probing -Spin Correlations in Optical Lattices
We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to -spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.Comment: 7 pages, 4 figure
Addendum to: Capillary floating and the billiard ball problem
We compare the results of our earlier paper on the floating in neutral
equilibrium at arbitrary orientation in the sense of Finn-Young with the
literature on its counterpart in the sense of Archimedes. We add a few remarks
of personal and social-historical character.Comment: This is an addendum to my article Capillary floating and the billiard
ball problem, Journal of Mathematical Fluid Mechanics 14 (2012), 363 -- 38
Enhanced Perturbative Continuous Unitary Transformations
Unitary transformations are an essential tool for the theoretical
understanding of many systems by mapping them to simpler effective models. A
systematically controlled variant to perform such a mapping is a perturbative
continuous unitary transformation (pCUT) among others. So far, this approach
required an equidistant unperturbed spectrum. Here, we pursue two goals: First,
we extend its applicability to non-equidistant spectra with the particular
focus on an efficient derivation of the differential flow equations, which
define the enhanced perturbative continuous unitary transformation (epCUT).
Second, we show that the numerical integration of the flow equations yields a
robust scheme to extract data from the epCUT. The method is illustrated by the
perturbation of the harmonic oscillator with a quartic term and of the two-leg
spin ladders in the strong-rung-coupling limit for uniform and alternating rung
couplings. The latter case provides an example of perturbation around a
non-equidistant spectrum.Comment: 27 pages, 18 figures; separated methodological background from
introduction, added perturbed harmonic oscillator for additional
illustration, added explicit solution of deepCUT equation
Evaluation of the mean intensity of the P-odd mixing of nuclear compound states
A temperature version of the shell-optical-model approach for describing the
low-energy compound-to-compound transitions induced by external single-particle
fields is given. The approach is applied to evaluate the mean intensity of the
P-odd mixing of nuclear compound states. Unified description for the mixing and
electromagnetic transitions allows one to evaluate the mean intensity without
the use of free parameters. The valence-mechanism contribution to the mentioned
intensity is also evaluated. Calculation results are compared with the data
deduced from cross sections of relevant neutron-induced reactions.Comment: LaTeX, 10 page
Hidden order in bosonic gases confined in one dimensional optical lattices
We analyze the effective Hamiltonian arising from a suitable power series
expansion of the overlap integrals of Wannier functions for confined bosonic
atoms in a 1d optical lattice. For certain constraints between the coupling
constants, we construct an explicit relation between such an effective bosonic
Hamiltonian and the integrable spin- anisotropic Heisenberg model. Therefore
the former results to be integrable by construction. The field theory is
governed by an anisotropic non linear -model with singlet and triplet
massive excitations; such a result holds also in the generic non-integrable
cases. The criticality of the bosonic system is investigated. The schematic
phase diagram is drawn. Our study is shedding light on the hidden symmetry of
the Haldane type for one dimensional bosons.Comment: 5 pages; 1 eps figure. Revised version, to be published in New. J.
Phy
Dynamical properties of ultracold bosons in an optical lattice
We study the excitation spectrum of strongly correlated lattice bosons for
the Mott-insulating phase and for the superfluid phase close to localization.
Within a Schwinger-boson mean-field approach we find two gapped modes in the
Mott insulator and the combination of a sound mode (Goldstone) and a gapped
(Higgs) mode in the superfluid. To make our findings comparable with
experimental results, we calculate the dynamic structure factor as well as the
linear response to the optical lattice modulation introduced by Stoeferle et
al. [Phys. Rev. Lett. 92, 130403 (2004)]. We find that the puzzling finite
frequency absorption observed in the superfluid phase could be explained via
the excitation of the gapped (Higgs) mode. We check the consistency of our
results with an adapted f-sum-rule and propose an extension of the experimental
technique by Stoeferle et al. to further verify our findings.Comment: 13 pages, 5 figure
Enhanced Electron Pairing in a Lattice of Berry Phase Molecules
We show that electron hopping in a lattice of molecules possessing a Berry
phase naturally leads to pairing. Our building block is a simple molecular site
model inspired by C, but realized in closer similarity with Na. In
the resulting model electron hopping must be accompanied by orbital operators,
whose function is to switch on and off the Berry phase as the electron number
changes. The effective hamiltonians (electron-rotor and electron-pseudospin)
obtained in this way are then shown to exhibit a strong pairing phenomenon, by
means of 1D linear chain case studies. This emerges naturally from numerical
studies of small -site rings, as well as from a BCS-like mean-field theory
formulation. The pairing may be explained as resulting from the exchange of
singlet pairs of orbital excitations, and is intimately connected with the
extra degeneracy implied by the Berry phase when the electron number is odd.
The relevance of this model to fullerides, to other molecular superconductors,
as well as to present and future experiments, is discussed.Comment: 30 pages, RevTe
Schwinger-boson approach to quantum spin systems: Gaussian fluctuactions in the "natural" gauge
We compute the Gaussian-fluctuation corrections to the saddle-point
Schwinger-boson results using collective coordinate methods. Concrete
application to investigate the frustrated J1-J2 antiferromagnet on the square
lattice shows that, unlike the saddle-point predictions, there is a quantum
nonmagnetic phase for 0.53 < J2/J1 < 0.64. This result is obtained by
considering the corrections to the spin stiffness on large lattices and
extrapolating to the thermodynamic limit, which avoids the infinite-lattice
infrared divergencies associated to Bose condensation. The very good agreement
of our results with exact numerical values on finite clusters lends support to
the calculational scheme employed.Comment: 4 pages, Latex, 3 figures included as eps files,minor correction
- …