2,508 research outputs found
Non-random dispersal in the butterfly Maniola jurtina: implications for metapopulation models
The dispersal patterns of animals are important in metapopulation ecology because they affect the dynamics and survival of populations. Theoretical models assume random dispersal but little is known in practice about the dispersal behaviour of individual animals or the strategy by which dispersers locate distant habitat patches. In the present study, we released individual meadow brown butterflies (Maniola jurtina) in a non-habitat and investigated their ability to return to a suitable habitat. The results provided three reasons for supposing that meadow brown butterflies do not seek habitat by means of random flight. First, when released within the range of their normal dispersal distances, the butterflies orientated towards suitable habitat at a higher rate than expected at random. Second, when released at larger distances from their habitat, they used a non-random, systematic, search strategy in which they flew in loops around the release point and returned periodically to it. Third, butterflies returned to a familiar habitat patch rather than a non-familiar one when given a choice. If dispersers actively orientate towards or search systematically for distant habitat, this may be problematic for existing metapopulation models, including models of the evolution of dispersal rates in metapopulations
Effect of Quadratic Zeeman Energy on the Vortex of Spinor Bose-Einstein Condensates
The spinor Bose-Einstein condensate of atomic gases has been experimentally
realized by a number of groups. Further, theoretical proposals of the possible
vortex states have been sugessted. This paper studies the effects of the
quadratic Zeeman energy on the vortex states. This energy was ignored in
previous theoretical studies, although it exists in experimental systems. We
present phase diagrams of various vortex states taking into account the
quadratic Zeeman energy. The vortex states are calculated by the
Gross-Pitaevskii equations. Several new kinds of vortex states are found. It is
also found that the quadratic Zeeman energy affects the direction of total
magnetization and causes a significant change in the phase diagrams.Comment: 6 pages, 5 figures. Published in J. Phys. Soc. Jp
Coreless vortex ground state of the rotating spinor condensate
We study the ground state of the rotating spinor condensate and show that for
slow rotation the ground state of the ferromagnetic spinor condensate is a
coreless vortex. While coreless vortex is not topologically stable, we show
that there is an energetic threshold for the creation of a coreless vortex.
This threshold corresponds to a critical rotation frequency that vanishes as
the system size increases. Also, we demonstrate the dramatically different
behavior of the spinor condensate with anti-ferromagnetic interactions. For
anti-ferromagnetic spinor condensate the angular momentum as a function of
rotation frequency exhibits the familiar staircase behavior, but in contrast to
an ordinary condensate the first step is to the state with angular momentum 1/2
per particle.Comment: v2: Numerical parameters for trapping frequency in z-direction and
for the particle number changed. Two new citations added ([13] and [22]).
More discussion in chapter III A. added. A new Figure 4 added, former figure
4 changed to Figure
Quantum Monte Carlo study of quasi-one-dimensional Bose gases
We study the behavior of quasi-one-dimensional (quasi-1d) Bose gases by Monte
Carlo techniques, i.e., by the variational Monte Carlo, the diffusion Monte
Carlo, and the fixed-node diffusion Monte Carlo technique. Our calculations
confirm and extend our results of an earlier study [Astrakharchik et al.,
cond-mat/0308585]. We find that a quasi-1d Bose gas i) is well described by a
1d model Hamiltonian with contact interactions and renormalized coupling
constant; ii) reaches the Tonks-Girardeau regime for a critical value of the 3d
scattering length a_3d; iii) enters a unitary regime for |a_3d| -> infinity,
where the properties of the gas are independent of a_3d and are similar to
those of a 1d gas of hard-rods; and iv) becomes unstable against cluster
formation for a critical value of the 1d gas parameter. The accuracy and
implications of our results are discussed in detail.Comment: 15 pages, 9 figure
Exploring quantum criticality based on ultracold atoms in optical lattices
Critical behavior developed near a quantum phase transition, interesting in
its own right, offers exciting opportunities to explore the universality of
strongly-correlated systems near the ground state. Cold atoms in optical
lattices, in particular, represent a paradigmatic system, for which the quantum
phase transition between the superfluid and Mott insulator states can be
externally induced by tuning the microscopic parameters. In this paper, we
describe our approach to study quantum criticality of cesium atoms in a
two-dimensional lattice based on in situ density measurements. Our research
agenda involves testing critical scaling of thermodynamic observables and
extracting transport properties in the quantum critical regime. We present and
discuss experimental progress on both fronts. In particular, the thermodynamic
measurement suggests that the equation of state near the critical point follows
the predicted scaling law at low temperatures.Comment: 15 pages, 6 figure
Rotating spin-1 bosons in the lowest Landau level
We present results for the ground states of a system of spin-1 bosons in a
rotating trap. We focus on the dilute, weakly interacting regime, and restrict
the bosons to the quantum states in the lowest Landau level (LLL) in the plane
(disc), sphere or torus geometries. We map out parts of the zero temperature
phase diagram, using both exact quantum ground states and LLL mean field
configurations. For the case of a spin-independent interaction we present exact
quantum ground states at angular momentum . For general values of the
interaction parameters, we present mean field studies of general ground states
at slow rotation and of lattices of vortices and skyrmions at higher rotation
rates. Finally, we discuss quantum Hall liquid states at ultra-high rotation.Comment: 24 pages, 14 figures, RevTe
Bosons and Fermions near Feshbach resonances
Near Feshbach resonances, , systems of Bose and Fermi particles
become strongly interacting/dense. In this unitary limit both bosons and
fermions have very different properties than in a dilute gas, e.g., the energy
per particle approach a value times an universal many-body
constant. Calculations based upon an approximate Jastrow wave function can
quantitatively describe recent measurements of trapped Bose and Fermi atoms
near Feshbach resonances.
The pairing gap between attractive fermions also scales as
near Feshbach resonances and is a large fraction
of the Fermi energy - promising for observing BCS superfluidity in traps.
Pairing undergoes several transitions depending on interaction strength and the
number of particles in the trap and can also be compared to pairing in nuclei.Comment: Revised version extended to include recent molecular BEC-BCS result
Observation of metastable states in spinor Bose-Einstein condensates
Bose-Einstein condensates have been prepared in long-lived metastable excited
states. Two complementary types of metastable states were observed. The first
is due to the immiscibility of multiple components in the condensate, and the
second to local suppression of spin-relaxation collisions. Relaxation via
re-condensation of non-condensed atoms, spin relaxation, and quantum tunneling
was observed. These experiments were done with F=1 spinor Bose-Einstein
condensates of sodium confined in an optical dipole trap.Comment: 3 figures included in paper, fourth figure separat
Vortex lattice of a Bose-Einstein Condensate in a rotating anisotropic trap
We study the vortex lattices in a Bose-Einstein Condensate in a rotating
anisotropic harmonic trap. We first investigate the single particle
wavefunctions obtained by the exact solution of the problem and give simple
expressions for these wavefunctions in the small anisotropy limit. Depending on
the strength of the interactions, a few or a large number of vortices can be
formed. In the limit of many vortices, we calculate the density profile of the
cloud and show that the vortex lattice stays triangular. We also find that the
vortex lattice planes align themselves with the weak axis of the external
potential. For a small number of vortices, we numerically solve the
Gross-Pitaevskii equation and find vortex configurations that are very
different from the vortex configurations in an axisymmetric rotating trap.Comment: 15 pages,4 figure
Energies and damping rates of elementary excitations in spin-1 Bose-Einstein condensed gases
Finite temperature Green's function technique is used to calculate the
energies and damping rates of elementary excitations of the homogeneous,
dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature both
in the density and spin channels. For this purpose the self-consistent
dynamical Hartree-Fock model is formulated, which takes into account the direct
and exchange processes on equal footing by summing up certain classes of
Feynman diagrams. The model is shown to fulfil the Goldstone theorem and to
exhibit the hybridization of one-particle and collective excitations correctly.
The results are applied to the gases of ^{23}Na and ^{87}Rb atoms.Comment: 26 pages, 21 figures. Added 2 new figures, detailed discussio
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