4,828 research outputs found
Stability, effective dimensions, and interactions for bosons in deformed fields
The hyperspherical adiabatic method is used to derive stability criteria for
Bose-Einstein condensates in deformed external fields. An analytical
approximation is obtained. For constant volume the highest stability is found
for spherical traps. Analytical approximations to the stability criterion with
and without zero point motion are derived. Extreme geometries of the field
effectively confine the system to dimensions lower than three. As a function of
deformation we compute the dimension to vary continuously between one and
three. We derive a dimension-dependent effective radial Hamiltonian and
investigate one choice of an effective interaction in the deformed case.Comment: 7 pages, 5 figures, submitted to Phys. Rev. A. In version 2 figures 2
and 5 are added along with more discussions and explanations. Version 3
contains added comments and reference
Condensates and correlated boson systems
We study two-body correlations in a many-boson system with a hyperspherical
approach, where we can use arbitrary scattering length and include two-body
bound states. As a special application we look on Bose-Einstein condensation
and calculate the stability criterium in a comparison with the experimental
criterium and the theoretical criterium from the Gross-Pitaevskii equation.Comment: 6 pages, 4 figures. Contribution to Workshop on Critical Stability
III in Trento. Submitted to Few-Body System
Stability and structure of two coupled boson systems in an external field
The lowest adiabatic potential expressed in hyperspherical coordinates is
estimated for two boson systems in an external harmonic trap. Corresponding
conditions for stability are investigated and the related structures are
extracted for zero-range interactions. Strong repulsion between non-identical
particles leads to two new features, respectively when identical particles
attract or repel each other. For repulsion new stable structures arise with
displaced center of masses. For attraction the mean-field stability region is
restricted due to motion of the center of masses
Effective Hamiltonian Theory and Its Applications in Quantum Information
This paper presents a useful compact formula for deriving an effective
Hamiltonian describing the time-averaged dynamics of detuned quantum systems.
The formalism also works for ensemble-averaged dynamics of stochastic systems.
To illustrate the technique we give examples involving Raman processes,
Bloch-Siegert shifts and Quantum Logic Gates.Comment: 5 pages, 3 figures, to be published in Canadian Journal of Physic
The primordial deuterium abundance at z = 2.504 from a high signal-to-noise spectrum of Q1009+2956
The spectrum of the quasar Q1009+2956 has been observed
extensively on the Keck telescope. The Lyman limit absorption system was previously used to measure D/H by Burles & Tytler using a
spectrum with signal to noise approximately 60 per pixel in the continuum near
Ly {\alpha} at . The larger dataset now available combines
to form an exceptionally high signal to noise spectrum, around 147 per pixel.
Several heavy element absorption lines are detected in this LLS, providing
strong constraints on the kinematic structure. We explore a suite of absorption
system models and find that the deuterium feature is likely to be contaminated
by weak interloping Ly {\alpha} absorption from a low column density H I cloud,
reducing the expected D/H precision. We find D/H =
for this system. Combining this new
measurement with others from the literature and applying the method of Least
Trimmed Squares to a statistical sample of 15 D/H measurements results in a
"reliable" sample of 13 values. This sample yields a primordial deuterium
abundance of (D/H). The
corresponding mean baryonic density of the Universe is . The quasar absorption data is of the same precision as, and
marginally inconsistent with, the 2015 CMB Planck (TT+lowP+lensing)
measurement, . Further quasar and more
precise nuclear data are required to establish whether this is a random
fluctuation.Comment: accepted by MNRAS, 18 pages, 12 figures, 6 table
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