1,056 research outputs found
BCS-BEC crossover in bilayers of cold fermionic polar molecules
We investigate the quantum and thermal phase diagram of fermionic polar molecules loaded in a bilayer trapping potential with perpendicular dipole moment. We use both a BCS-theory approach that is most reliable at weak coupling and a strong-coupling approach that considers the two-body bound dimer states with one molecule in each layer as the relevant degree of freedom. The system ground state is a Bose-Einstein condensate (BEC) of dimer bound states in the low-density limit and a paired superfluid (BCS) state in the high-density limit. At zero temperature, the intralayer repulsion is found to broaden the regime of BCS-BEC crossover and can potentially induce system collapse through the softening of roton excitations. The BCS theory and the strongly coupled dimer picture yield similar predictions for the parameters of the crossover regime. The Berezinskii-Kosterlitz-Thouless transition temperature of the dimer superfluid is also calculated. The crossover can be driven by many-body effects and is strongly affected by the intralayer interaction which was ignored in previous studies
Assessing the accuracy of Hartree-Fock-Bogoliubov calculations by use of mass relations
The accuracy of three different sets of Hartree-Fock-Bogoliubov calculations
of nuclear binding energies is systematically evaluated. To emphasize minor
fluctuations, a second order, four-point mass relation, which almost completely
eliminates smooth aspects of the binding energy, is introduced. Applying this
mass relation yields more scattered results for the calculated binding
energies. By examining the Gaussian distributions of the non-smooth aspects
which remain, structural differences can be detected between measured and
calculated binding energies. Substructures in regions of rapidly changing
deformation, specifically around and , are clearly
seen for the measured values, but are missing from the calculations. A similar
three-point mass relation is used to emphasize odd-even effects. A clear
decrease with neutron excess is seen continuing outside the experimentally
known region for the calculations.Comment: 13 pages, 9 figures, published versio
Review and analysis of the DNW/Model 360 rotor acoustic data base
A comprehensive model rotor aeroacoustic data base was collected in a large anechoic wind tunnel in 1986. Twenty-six microphones were positioned around the azimuth to collect acoustic data for approximately 150 different test conditions. A dynamically scaled, blade-pressure-instrumented model of the forward rotor of the BH360 helicopter simultaneously provided blade pressures for correlation with the acoustic data. High-speed impulsive noise, blade-vortex interaction noise, low-frequency noise, and broadband noise were all captured in this extensive data base. Trends are presentes for each noise source, with important parametric variations. The purpose of this paper is to introduce this data base and illustrate its potential for predictive code validation
Model independence in two dimensions and polarized cold dipolar molecules
We calculate the energy and wave functions of two particles confined to two
spatial dimensions interacting via arbitrary anisotropic potentials with
negative or zero net volume. The general rigorous analytic expressions are
given in the weak coupling limit where universality or model independence are
approached. The monopole part of anisotropic potentials is crucial in the
universal limit. We illustrate the universality with a system of two
arbitrarily polarized cold dipolar molecules in a bilayer. We discuss the
transition to universality as function of polarization and binding energy, and
compare analytic and numerical results obtained by the stochastic variational
method. The universal limit is essentially reached for experimentally
accessible strengths.Comment: 4.1 pages, 3 figures, published versio
Engineering the Dynamics of Effective Spin-Chain Models for Strongly Interacting Atomic Gases
We consider a one-dimensional gas of cold atoms with strong contact
interactions and construct an effective spin-chain Hamiltonian for a
two-component system. The resulting Heisenberg spin model can be engineered by
manipulating the shape of the external confining potential of the atomic gas.
We find that bosonic atoms offer more flexibility for tuning independently the
parameters of the spin Hamiltonian through interatomic (intra-species)
interaction which is absent for fermions due to the Pauli exclusion principle.
Our formalism can have important implications for control and manipulation of
the dynamics of few- and many-body quantum systems; as an illustrative example
relevant to quantum computation and communication, we consider state transfer
in the simplest non-trivial system of four particles representing
exchange-coupled qubits.Comment: 10 pages including appendix, 3 figures, revised versio
Bound States and Universality in Layers of Cold Polar Molecules
The recent experimental realization of cold polar molecules in the rotational
and vibrational ground state opens the door to the study of a wealth of
phenomena involving long-range interactions. By applying an optical lattice to
a gas of cold polar molecules one can create a layered system of planar traps.
Due to the long-range dipole-dipole interaction one expects a rich structure of
bound complexes in this geometry. We study the bilayer case and determine the
two-body bound state properties as a function of the interaction strength. The
results clearly show that a least one bound state will always be present in the
system. In addition, bound states at zero energy show universal behavior and
extend to very large radii. These results suggest that non-trivial bound
complexes of more than two particles are likely in the bilayer and in more
complicated chain structures in multi-layer systems.Comment: 6 pages, 5 figures. Revised version to be publishe
Hyperspherical Treatment of Strongly-Interacting Few-Fermion Systems in One Dimension
We examine a one-dimensional two-component fermionic system in a trap,
assuming that all particles have the same mass and interact through a strong
repulsive zero-range force. First we show how a simple system of three strongly
interacting particles in a harmonic trap can be treated using the
hyperspherical formalism. Next we discuss the behavior of the energy for the
N-body system.Comment: 5 pages. Original paper for EPJ ST in connection with the workshop
BEC2014 28-31 May 2014 in Levico Terme, Ital
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