9,541 research outputs found
Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well
We consider an atomic Bose-Einstein condensate trapped in a symmetric
one-dimensional double well potential in the four-mode approximation and show
that the semiclassical dynamics of the two ground state modes can be strongly
influenced by a macroscopic occupation of the two excited modes. In particular,
the addition of the two excited modes already unveils features related to the
effect of dissipation on the condensate. In general, we find a rich dynamics
that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping,
chaotic behavior, and the existence of fixed points. We investigate how the
dynamics of the atoms in the excited modes can be manipulated by controlling
the atomic populations of the ground states.Comment: 12 pages, 5 figure
Stretched chemical bonds in Si6H6: A transition from ring currents to localized pi-electrons?
Motivated by solid-state studies on the cleavage force in Si, and the
consequent stretching of chemical bonds, we here study bond stretching in the,
as yet unsynthesized, free space molecule Si6H6. We address the question as to
whether substantial bond stretching (but constrained to uniform scaling on all
bonds) can result in a transition from ring current behaviour, characteristic
say of benzene at its equilibrium geometry, to localized pi-electrons on Si
atoms. Some calculations are also recorded on dissociation into 6 SiH radicals.
While the main studies have been carried out by unrestricted Hartree-Fock (HF)
theory, the influence of electron correlation has been examined using two forms
of density functional theory. Planar Si6H6 treated by HF is bound to be
unstable, not all vibrational frequencies being real. Some buckling is then
allowed, which results in real frequencies and stability. Evidence is then
provided that the non-planar structure, as the Si-Si distance is increased,
exhibits pi-electron localization in the range 1.2-1.5 times the equilibrium
distance
Funding Shortfall for Housing Vouchers Could Have Serious Health Consequences for Children
In the fourth brief in its Policy Action series, Children's HealthWatch finds that unaffordable housing endangers the health and development of young children. Due to a federal funding shortfall, state and local housing agencies will be forced to reduce or eliminate rental assitance to thousands of families starting this month. Voucher cuts will push more families into the ranks of the "hidden homeless" -- families that move frequently, crowd into apartments that are too small, or live doubled up with other households when they cannot find affordable housing. Children in hidden homeless families are at increased risk for poor health, nutrition, and growth, as well as developmental delays. Timely Congressional action to protect the Housing Choice Voucher Program will ensure that families have stable, affordable housing essential to children's health
A Three Dimensional Lattice of Ion Traps
We propose an ion trap configuration such that individual traps can be
stacked together in a three dimensional simple cubic arrangement. The isolated
trap as well as the extended array of ion traps are characterized for different
locations in the lattice, illustrating the robustness of the lattice of traps
concept. Ease in the addressing of ions at each lattice site, individually or
simultaneously, makes this system naturally suitable for a number of
experiments. Application of this trap to precision spectroscopy, quantum
information processing and the study of few particle interacting system are
discussed.Comment: 4 pages, 4 Figures. Fig 1 appears as a composite of 1a, 1b, 1c and
1d. Fig 2 appears as a composite of 2a, 2b and 2
Parity Violation in Aharonov-Bohm Systems: The Spontaneous Hall Effect
We show how macroscopic manifestations of (and ) symmetry breaking can
arise in a simple system subject to Aharonov-Bohm interactions. Specifically,
we study the conductivity of a gas of charged particles moving through a dilute
array of flux tubes. The interaction of the electrons with the flux tubes is
taken to be of a purely Aharonov-Bohm type. We find that the system exhibits a
non-zero transverse conductivity, i.e., a spontaneous Hall effect. This is in
contrast with the fact that the cross sections for both scattering and
bremsstrahlung (soft photon emission) of a single electron from a flux tube are
invariant under reflections. We argue that the asymmetry in the conductivity
coefficients arises from many-body effects. On the other hand, the transverse
conductivity has the same dependence on universal constants that appears in the
Quantum Hall Effect, a result that we relate to the validity of the Mean Field
approximation.Comment: 12 pages (4 figures available upon request), RevTex, EHU-FT-93/1
Spatial fluctuations in an optical parametric oscillator below threshold with an intracavity photonic crystal
We show how to control spatial quantum correlations in a multimode degenerate
optical parametric oscillator type I below threshold by introducing a spatially
inhomogeneous medium, such as a photonic crystal, in the plane perpendicular to
light propagation. We obtain the analytical expressions for all the
correlations in terms of the relevant parameters of the problem and study the
number of photons, entanglement, squeezing, and twin beams. Considering
different regimes and configurations we show the possibility to tune the
instability thresholds as well as the quantumness of correlations by breaking
the translational invariance of the system through a photonic crystal
modulation.Comment: 12 pages, 7 figure
TeV scale resonant leptogenesis from supersymmetry breaking
We propose a model of TeV-scale resonant leptogenesis based upon recent
models of the generation of light neutrino masses from supersymmetry-breaking
effects with TeV-scale right-handed (rhd) neutrinos, . The model leads to
naturally large cosmological lepton asymmetries via the resonant behaviour of
the one-loop self-energy contribution to decay. Our model addresses the
primary problems of previous phenomenological studies of low-energy
leptogenesis: a rational for TeV-scale rhd neutrinos with small Yukawa
couplings so that the out-of equilibrium condition for decay is
satisfied; the origin of the tiny, but non-zero mass splitting required between
at least two masses; and the necessary non-trivial breaking of flavour
symmetries in the rhd neutrino sector. The low mass-scale of the rhd neutrinos
and their superpartners, and the TeV-scale -terms automatically contained
within the model offer opportunities for partial direct experimental tests of
this leptogenesis mechanism at future colliders.Comment: 10 Pages latex, version for JHE
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