183 research outputs found
Spin textures in condensates with large dipole moments
We have solved numerically the ground states of a Bose-Einstein condensate in
the presence of dipolar interparticle forces using a semiclassical approach.
Our motivation is to model, in particular, the spontaneous spin textures
emerging in quantum gases with large dipole moments, such as 52Cr or Dy
condensates, or ultracold gases consisting of polar molecules. For a
pancake-shaped harmonic (optical) potential, we present the ground state phase
diagram spanned by the strength of the nonlinear coupling and dipolar
interactions. In an elongated harmonic potential, we observe a novel helical
spin texture. The textures calculated according to the semiclassical model in
the absence of external polarizing fields are predominantly analogous to
previously reported results for a ferromagnetic F = 1 spinor Bose-Einstein
condensate, suggesting that the spin textures arising from the dipolar forces
are largely independent of the value of the quantum number F or the origin of
the dipolar interactions.Comment: 9 pages, 6 figure
Giant Vortex Lattice Deformations in Rapidly Rotating Bose-Einstein Condensates
We have performed numerical simulations of giant vortex structures in rapidly
rotating Bose-Einstein condensates within the Gross-Pitaevskii formalism. We
reproduce the qualitative features, such as oscillation of the giant vortex
core area, formation of toroidal density hole, and the precession of giant
vortices, observed in the recent experiment [Engels \emph{et.al.}, Phys. Rev.
Lett. {\bf 90}, 170405 (2003)]. We provide a mechanism which quantitatively
explains the observed core oscillation phenomenon. We demonstrate the clear
distinction between the mechanism of atom removal and a repulsive pinning
potential in creating giant vortices. In addition, we have been able to
simulate the transverse Tkachenko vortex lattice vibrations.Comment: 5 pages, 6 figures; revised description of core oscillation, new
subfigur
Stable Fractional Vortices in the Cyclic States of Bose-Einstein Condensates
We propose methods to create fractional vortices in the cyclic state of an F
= 2 spinor Bose-Einstein condensate by manipulating its internal spin structure
using pulsed microwave and laser fields. The stability of such vortices is
studied as a function of the rotation frequency of the confining harmonic trap
both in pancake and cigar shaped condensates. We find a range of parameters for
which the so-called 1/3-vortex state is energetically favorable. Such
fractional vortices could be created in condensates of 87Rb atoms using current
experimental techniques facilitating probing of topological defects with
non-Abelian statistics.Comment: 5 pages, 2 figure
Angular momentum exchange between coherent light and matter fields
Full, three dimensional, time-dependent simulations are presented
demonstrating the quantized transfer of angular momentum to a Bose-Einstein
condensate from a laser carrying orbital angular momentum in a
Laguerre-Gaussian mode. The process is described in terms of coherent Bragg
scattering of atoms from a chiral optical lattice. The transfer efficiency and
the angular momentum content of the output coupled vortex state are analyzed
and compared with a recent experiment.Comment: 4 pages, 4 figure
Quantum Monte Carlo Study of Positron Lifetimes in Solids
Publisher Copyright: © 2022 American Physical Society.We present an analysis of positron lifetimes in solids with unprecedented depth. Instead of modeling correlation effects with density functionals, we study positron-electron wave functions with long-range correlations included. This gives new insight in understanding positron annihilation in metals, insulators, and semiconductors. By using a new quantum Monte Carlo approach for computation of positron lifetimes, an improved accuracy compared to previous computations is obtained for a representative set of materials when compared with experiment. Thus, we present a method without free parameters as a useful alternative to the already existing methods for modeling positrons in solids.Peer reviewe
Quantum Monte Carlo Study of Positron Lifetimes in Solids
Publisher Copyright: © 2022 American Physical Society.We present an analysis of positron lifetimes in solids with unprecedented depth. Instead of modeling correlation effects with density functionals, we study positron-electron wave functions with long-range correlations included. This gives new insight in understanding positron annihilation in metals, insulators, and semiconductors. By using a new quantum Monte Carlo approach for computation of positron lifetimes, an improved accuracy compared to previous computations is obtained for a representative set of materials when compared with experiment. Thus, we present a method without free parameters as a useful alternative to the already existing methods for modeling positrons in solids.Peer reviewe
Decay constants of heavy pseudoscalar mesons from QCD sum rules
We revisit the sum-rule extraction of the decay constants of the D, Ds, B,
and Bs mesons from the two-point correlator of heavy-light pseudoscalar
currents. We use the operator product expansion for this correlator expressed
in terms of the MSbar heavy-quark mass, for which the perturbative expansion
exhibits a reasonable convergence. Our main emphasis is laid on the control
over the uncertainties in the decay constants, related both to the input QCD
parameters and to the limited accuracy of the method of sum-rules. This becomes
possible due to the application of our procedure of extracting hadron
observables that involves as novel feature dual thresholds depending on the
Borel parameter. For charmed mesons, we find the decay constants f_D=206.2\pm
7.3(OPE)\pm 5.1(syst) MeV and f_Ds=245.3\pm 15.7(OPE)\pm 4.5(syst) MeV. For
beauty mesons, the decay constants turn out to be extremely sensitive to the
precise value of mb(mb). By requiring our sum-rule estimate to match the
average of the lattice results for f_B, a very accurate value mb(mb)=4.245\pm
0.025 GeV is extracted, leading to f_B=193.4\pm 12.3(OPE)\pm 4.3(syst) MeV and
f_Bs=232.5\pm 18.6(OPE)\pm 2.4(syst) MeV.Comment: 12 page
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