4,510 research outputs found
Paleobiology and behavior
Paleobiology, the study of ancient life, gives us a window onto the habits, biology, and behavior of individuals and species that are now extinct. Although extinct species cannot be observed directly, their paleobiology and behavior can be inferred from study of the fossil and geological records in combination with knowledge about modern organisms and processes. Paleobiological reconstructions thus help to shed light on many aspects of ancient lives, including ecology, diet, locomotion, life history, mating systems, biogeography, speciation, extinction, and abundance
Female brain size affects the assessment of male attractiveness during mate choice
Mate choice decisions are central in sexual selection theory aimed to understand how sexual traits evolve and their role in evolutionary diversification. We test the hypothesis that brain size and cognitive ability are important for accurate assessment of partner quality and that variation in brain size and cognitive ability underlies variation in mate choice. We compared sexual preference in guppy female lines selected for divergence in relative brain size, which we have previously shown to have substantial differences in cognitive ability. In a dichotomous choice test, large-brained and wild-type females showed strong preference for males with color traits that predict attractiveness in this species. In contrast, small-brained females showed no preference for males with these traits. In-depth analysis of optomotor response to color cues and gene expression of key opsins in the eye revealed that the observed differences were not due to differences in visual perception of color, indicating that differences in the ability to process indicators of attractiveness are responsible. We thus provide the first experimental support that individual variation in brain size affects mate choice decisions and conclude that differences in cognitive ability may be an important underlying mechanism behind variation in female mate choice
Density Waves in Layered Systems with Fermionic Polar Molecules
A layered system of two-dimensional planes containing fermionic polar
molecules can potentially realize a number of exotic quantum many-body states.
Among the predictions, are density-wave instabilities driven by the anisotropic
part of the dipole-dipole interaction in a single layer. However, in typical
multilayer setups it is reasonable to expect that the onset and properties of a
density-wave are modified by adjacent layers. Here we show that this is indeed
the case. For multiple layers the critical strength for the density-wave
instability decreases with the number of layers. The effect depends on density
and is more pronounced in the low density regime. The lowest solution of the
instability corresponds to the density waves in the different layers being
in-phase, whereas higher solutions have one or several adjancet layers that are
out of phase. The parameter regime needed to explore this instability is within
reach of current experiments.Comment: 7 pages, 4 figures. Final version in EPJD, EuroQUAM special issue
"Cold Quantum Matter - Achievements and Prospects
Optical Bragg, atom Bragg and cavity QED detections of quantum phases and excitation spectra of ultracold atoms in bipartite and frustrated optical lattices
Ultracold atoms loaded on optical lattices can provide unprecedented
experimental systems for the quantum simulations and manipulations of many
quantum phases and quantum phase transitions between these phases. However, so
far, how to detect these quantum phases and phase transitions effectively
remains an outstanding challenge. In this paper, we will develop a systematic
and unified theory of using the optical Bragg scattering, atomic Bragg
scattering or cavity QED to detect the ground state and the excitation spectrum
of many quantum phases of interacting bosons loaded in bipartite and frustrated
optical lattices.
We show that the two photon Raman transition processes in the three detection
methods not only couple to the density order parameter, but also the {\sl
valence bond order} parameter due to the hopping of the bosons on the lattice.
This valence bond order coupling is very sensitive to any superfluid order or
any Valence bond (VB) order in the quantum phases to be probed. These quantum
phases include not only the well known superfluid and Mott insulating phases,
but also other important phases such as various kinds of charge density waves
(CDW), valence bond solids (VBS), CDW-VBS phases with both CDW and VBS orders
unique to frustrated lattices, and also various kinds of supersolids.
The physical measurable quantities of the three experiments are the light
scattering cross sections, the atom scattered clouds and the cavity leaking
photons respectively. We analyze respectively the experimental conditions of
the three detection methods to probe these various quantum phases and their
corresponding excitation spectra. We also address the effects of a finite
temperature and a harmonic trap.Comment: REVTEX4-1, 32 pages, 16.eps figures, to Appear in Annals of Physic
Core repulsion effects in alkali trimers
The present paper is related to a talk presented during the Symposium on
Coherent Control and Ultracold Chemistry held during the Sixth Congress of the
International Society for Theoretical Chemical Physics (ISTCP-VI, July 2008).
The talk was entitled "Electronic structure properties of alkali dimers and
trimers. Prospects for alignment of ultracold molecules". Here we report on the
electrostatic repulsion forces of the ionic cores at short separation, involved
when the potential energy surfaces of alkali trimers are calculated with a
quantum chemistry approach based on effective large-core potentials for ionic
core description. We demonstrate that such forces in the triatomic molecule can
be obtained as the sum of three pairwise terms. We illustrate our results on
the lowest electronic states of Cs, which are computed for the first time
within a full configuration interaction based on a large Gaussian basis set. As
a preliminary section, we also propose a brief introduction about the
importance of alkali trimer systems in the context of cold and ultracold
molecules
Thermodynamics of Dipolar Chain Systems
The thermodynamics of a quantum system of layers containing perpendicularly
oriented dipolar molecules is studied within an oscillator approximation for
both bosonic and fermionic species. The system is assumed to be built from
chains with one molecule in each layer. We consider the effects of the
intralayer repulsion and quantum statistical requirements in systems with more
than one chain. Specifically, we consider the case of two chains and solve the
problem analytically within the harmonic Hamiltonian approach which is accurate
for large dipole moments. The case of three chains is calculated numerically.
Our findings indicate that thermodynamic observables, such as the heat
capacity, can be used to probe the signatures of the intralayer interaction
between chains. This should be relevant for near future experiments on polar
molecules with strong dipole moments.Comment: 15 pages, 5 figures, final versio
Universal ultracold collision rates for polar molecules of two alkali-metal atoms
Universal collision rate constants are calculated for ultracold collisions of
two like bosonic or fermionic heteronuclear alkali-metal dimers involving the
species Li, Na, K, Rb, or Cs. Universal collisions are those for which the
short range probability of a reactive or quenching collision is unity such that
a collision removes a pair of molecules from the sample. In this case, the
collision rates are determined by universal quantum dynamics at very long range
compared to the chemical bond length. We calculate the universal rate constants
for reaction of the reactive dimers in their ground vibrational state and
for vibrational quenching of non-reactive dimers with . Using the
known dipole moments and estimated van der Waals coefficients of each species,
we calculate electric field dependent loss rate constants for collisions of
molecules tightly confined to quasi-two-dimensional geometry by a
one-dimensional optical lattice. A simple scaling relation of the
quasi-two-dimensional loss rate constants with dipole strength, trap frequency
and collision energy is given for like bosons or like fermions. It should be
possible to stabilize ultracold dimers of any of these species against
destructive collisions by confining them in a lattice and orienting them with
electric field of less than 20 kV/cm.Comment: 12 pages, 8 figure
Quantum Simulation of Antiferromagnetic Spin Chains in an Optical Lattice
Understanding exotic forms of magnetism in quantum mechanical systems is a
central goal of modern condensed matter physics, with implications from high
temperature superconductors to spintronic devices. Simulating magnetic
materials in the vicinity of a quantum phase transition is computationally
intractable on classical computers due to the extreme complexity arising from
quantum entanglement between the constituent magnetic spins. Here we employ a
degenerate Bose gas confined in an optical lattice to simulate a chain of
interacting quantum Ising spins as they undergo a phase transition. Strong spin
interactions are achieved through a site-occupation to pseudo-spin mapping. As
we vary an applied field, quantum fluctuations drive a phase transition from a
paramagnetic phase into an antiferromagnetic phase. In the paramagnetic phase
the interaction between the spins is overwhelmed by the applied field which
aligns the spins. In the antiferromagnetic phase the interaction dominates and
produces staggered magnetic ordering. Magnetic domain formation is observed
through both in-situ site-resolved imaging and noise correlation measurements.
By demonstrating a route to quantum magnetism in an optical lattice, this work
should facilitate further investigations of magnetic models using ultracold
atoms, improving our understanding of real magnetic materials.Comment: 12 pages, 9 figure
Formation and interactions of cold and ultracold molecules: new challenges for interdisciplinary physics
Progress on researches in the field of molecules at cold and ultracold
temperatures is reported in this review. It covers extensively the experimental
methods to produce, detect and characterize cold and ultracold molecules
including association of ultracold atoms, deceleration by external fields and
kinematic cooling. Confinement of molecules in different kinds of traps is also
discussed. The basic theoretical issues related to the knowledge of the
molecular structure, the atom-molecule and molecule-molecule mutual
interactions, and to their possible manipulation and control with external
fields, are reviewed. A short discussion on the broad area of applications
completes the review.Comment: to appear in Reports on Progress in Physic
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