2,724 research outputs found
Semiclassical approach to Bose-Einstein condensates in a triple well potential
We present a new approach for the analysis of Bose-Einstein condensates in a
few mode approximation. This method has already been used to successfully
analyze the vibrational modes in various molecular systems and offers a new
perspective on the dynamics in many particle bosonic systems. We discuss a
system consisting of a Bose-Einstein condensate in a triple well potential.
Such systems correspond to classical Hamiltonian systems with three degrees of
freedom. The semiclassical approach allows a simple visualization of the
eigenstates of the quantum system referring to the underlying classical
dynamics. From this classification we can read off the dynamical properties of
the eigenstates such as particle exchange between the wells and entanglement
without further calculations. In addition, this approach offers new insights
into the validity of the mean-field description of the many particle system by
the Gross-Pitaevskii equation, since we make use of exactly this correspondence
in our semiclassical analysis. We choose a three mode system in order to
visualize it easily and, moreover, to have a sufficiently interesting
structure, although the method can also be extended to higher dimensional
systems.Comment: 15 pages, 15 figure
Anomalous shell effect in the transition from a circular to a triangular billiard
We apply periodic orbit theory to a two-dimensional non-integrable billiard
system whose boundary is varied smoothly from a circular to an equilateral
triangular shape. Although the classical dynamics becomes chaotic with
increasing triangular deformation, it exhibits an astonishingly pronounced
shell effect on its way through the shape transition. A semiclassical analysis
reveals that this shell effect emerges from a codimension-two bifurcation of
the triangular periodic orbit. Gutzwiller's semiclassical trace formula, using
a global uniform approximation for the bifurcation of the triangular orbit and
including the contributions of the other isolated orbits, describes very well
the coarse-grained quantum-mechanical level density of this system. We also
discuss the role of discrete symmetry for the large shell effect obtained here.Comment: 14 pages REVTeX4, 16 figures, version to appear in Phys. Rev. E.
Qualities of some figures are lowered to reduce their sizes. Original figures
are available at http://www.phys.nitech.ac.jp/~arita/papers/tricirc
On the canonically invariant calculation of Maslov indices
After a short review of various ways to calculate the Maslov index appearing
in semiclassical Gutzwiller type trace formulae, we discuss a
coordinate-independent and canonically invariant formulation recently proposed
by A Sugita (2000, 2001). We give explicit formulae for its ingredients and
test them numerically for periodic orbits in several Hamiltonian systems with
mixed dynamics. We demonstrate how the Maslov indices and their ingredients can
be useful in the classification of periodic orbits in complicated bifurcation
scenarios, for instance in a novel sequence of seven orbits born out of a
tangent bifurcation in the H\'enon-Heiles system.Comment: LaTeX, 13 figures, 3 tables, submitted to J. Phys.
Super-shell structure in harmonically trapped fermionic gases and its semi-classical interpretation
It was recently shown in self-consistent Hartree-Fock calculations that a
harmonically trapped dilute gas of fermionic atoms with a repulsive two-body
interaction exhibits a pronounced {\it super-shell} structure: the shell
fillings due to the spherical harmonic trapping potential are modulated by a
beat mode. This changes the ``magic numbers'' occurring between the beat nodes
by half a period. The length and amplitude of the beating mode depends on the
strength of the interaction. We give a qualitative interpretation of the beat
structure in terms of a semiclassical trace formula that uniformly describes
the symmetry breaking U(3) SO(3) in a 3D harmonic oscillator potential
perturbed by an anharmonic term with arbitrary strength. We show
that at low Fermi energies (or particle numbers), the beating gross-shell
structure of this system is dominated solely by the two-fold degenerate
circular and (diametrically) pendulating orbits.Comment: Final version of procedings for the 'Nilsson conference
Closed orbits and spatial density oscillations in the circular billiard
We present a case study for the semiclassical calculation of the oscillations
in the particle and kinetic-energy densities for the two-dimensional circular
billiard. For this system, we can give a complete classification of all closed
periodic and non-periodic orbits. We discuss their bifurcations under variation
of the starting point r and derive analytical expressions for their properties
such as actions, stability determinants, momentum mismatches and Morse indices.
We present semiclassical calculations of the spatial density oscillations using
a recently developed closed-orbit theory [Roccia J and Brack M 2008 Phys. Rev.
Lett. 100 200408], employing standard uniform approximations from perturbation
and bifurcation theory, and test the convergence of the closed-orbit sum.Comment: LaTeX, 42 pp., 17 figures (24 *.eps files, 1 *.tex file); final
version (v3) to be published in J. Phys.
Bats of the Loess Hills Ecoregion of Southeast Nebraska
We surveyed bats at 49 sites in the Loess Hills Ecoregion of southeastern Nebraska, along the western edge of the eastern forest biome in eastern Richardson, Nemaha, and Otoe counties. We completed this study shortly before the northern long-eared bat (Myotis septentrionalis) was listed by the United States Fish and Wildlife Service under the Endangered Species Act. The expectation of listing, along with potential presence of the endangered Indiana bat (Myotis sodalis), motivated the study. We captured 183 bats of five species: eastern red bat (Lasiurus borealis) (n = 103; 56 %), big brown bat (Eptesicus fuscus) (n = 47; 26 %), evening bat (Nycticeius humeralis) (n = 27; 15 %), hoary bat (Lasiurus cinereus) (n = 4; 2 %), and northern long-eared bat (n = 2; 1 %). The mean catch per net site was 3.7 bats (SD = 4.8). The Eastern red bat was captured most commonly and at the most sites. We established the first record of this species from Nemaha County, with reproduction documented in all three counties. More reproductive female red bats were captured than adult males. Big brown bat captures consisted of approximately equal proportions adult males, reproductive females, and volant young of year. We established the first records for big brown bat reproduction in Otoe and Nemaha counties. Only reproductive female and juvenile evening bats were captured, with geographic and reproductive records established for all three counties. Captures of the hoary bat, a lactating female at one site and two juveniles at another, represented a Nemaha County geographic and reproductive record. We radio-tagged a non-reproductive female and an adult male northern long-eared bat from Otoe County and tracked them to roosts along the Missouri River, 3.43 and 2.03 km from the net site, respectively. We completed four emergence counts at each roost, with each bat exiting its respective roost on only one evening and neither bat visiting the other roost. We never documented more than three individuals exiting each roost on a given night. Overall, this study documented relatively low abundance, species richness, and species diversity when compared to studies in the eastern United States
Classical orbit bifurcation and quantum interference in mesoscopic magnetoconductance
We study the magnetoconductance of electrons through a mesoscopic channel
with antidots. Through quantum interference effects, the conductance maxima as
functions of the magnetic field strength and the antidot radius (regulated by
the applied gate voltage) exhibit characteristic dislocations that have been
observed experimentally. Using the semiclassical periodic orbit theory, we
relate these dislocations directly to bifurcations of the leading classes of
periodic orbits.Comment: 4 pages, including 5 figures. Revised version with clarified
discussion and minor editorial change
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