2,870 research outputs found
Tkachenko modes as sources of quasiperiodic pulsar spin variations
We study the long wavelength shear modes (Tkachenko waves) of triangular
lattices of singly quantized vortices in neutron star interiors taking into
account the mutual friction between the superfluid and the normal fluid and the
shear viscosity of the normal fluid. The set of Tkachenko modes that propagate
in the plane orthogonal to the spin vector are weakly damped if the coupling
between the superfluid and normal fluid is small. In strong coupling, their
oscillation frequencies are lower and are undamped for small and moderate shear
viscosities. The periods of these modes are consistent with the observed
~100-1000 day variations in spin of PSR 1828-11.Comment: 7 pages, 3 figures, uses RevTex, v2: added discussion/references,
matches published versio
Vortex lattice stability and phase coherence in three-dimensional rapidly rotating Bose condensates
We establish the general equations of motion for the modes of a vortex
lattice in a rapidly rotating Bose-Einstein condensate in three dimensions,
taking into account the elastic energy of the lattice and the vortex line
bending energy. As in two dimensions, the vortex lattice supports Tkachenko and
gapped sound modes. In contrast, in three dimensions the Tkachenko mode
frequency at long wavelengths becomes linear in the wavevector for any
propagation direction out of the transverse plane. We compute the correlation
functions of the vortex displacements and the superfluid order parameter for a
homogeneous Bose gas of bounded extent in the axial direction. At zero
temperature the vortex displacement correlations are convergent at large
separation, but at finite temperatures, they grow with separation. The growth
of the vortex displacements should lead to observable melting of vortex
lattices at higher temperatures and somewhat lower particle number and faster
rotation than in current experiments. At zero temperature a system of large
extent in the axial direction maintains long range order-parameter correlations
for large separation, but at finite temperatures the correlations decay with
separation.Comment: 10 pages, 2 figures, Changes include the addition of the particle
density - vortex density coupling and the correct value of the shear modulu
Energy losses of fast heavy-ion projectiles in dense hydrogen plasmas
It has been recently shown that the Bethe-Larkin formula for the energy
losses of fast heavy-ion projectiles in dense hydrogen plasmas is corrected by
the electron-ion correlations [Phys. Rev. Lett. \textbf{101}, 075002 (2008)].
We report numerical estimates of this correction based on the values of
obtained by numerical simulations in [Phys. Rev. E \textbf{61},
3470 (2000)]. We also extend this result to the case of projectiles with
dicluster charge distribution. We show that the experimental visibility of the
electron-ion correlation correction is enhanced in the case of dicluster
projectiles with randomly orientated charge centers. Although we consider here
the hydrogen plasmas to make the effect physically more clear, the
generalization to multispecies plasmas is straightforward.Comment: 5 pages, 1 figure. International Conference on Strongly Coupled
Coulomb Systems 2008, Camerino (Italy). To appear in J. Phys.
Complete polarization control for a nanofiber waveguide using directional coupling
Optical nanofiber waveguides are widely used for near-field delivery and
measurement of light. Despite their versatility and efficiency, nanofibers have
a critical drawback - their inability to maintain light's polarization state on
propagation. Here, we design a directional coupler consisting of two crossed
nanofibers to probe the polarization state at the waist region. Directionality
of coupling occurs due to asymmetric dipolar emission or spin-locking when the
evanescent field pattern breaks the mirror symmetry of the crossed-nanofiber
system. We demonstrate that, by monitoring the outputs from the directional
coupler, two non-orthogonal polarization states can be prepared at the
nanofiber waist with a fidelity higher than 99%. Based on these states, we
devise a simple and reliable method for complete control of the polarization
along a nanofiber waveguide.Comment: 8 pages, 8 figure
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