6,942 research outputs found
Universal four-body states in heavy-light mixtures with positive scattering length
The number of four-body states known to behave universally is small. This
work adds a new class of four-body states to this relatively short list. We
predict the existence of a universal four-body bound state for heavy-light
mixtures consisting of three identical heavy fermions and a fourth
distinguishable lighter particle with mass ratio and
short-range interspecies interaction characterized by a positive s-wave
scattering length. The structural properties of these universal states are
discussed and finite-range effects are analyzed. The bound states can be
experimentally realized and probed utilizing ultracold atom mixtures.Comment: 5 page
Threshold behavior of bosonic two-dimensional few-body systems
Bosonic two-dimensional self-bound clusters consisting of atoms
interacting through additive van der Waals potentials become unbound at a
critical mass m*(N); m*(N) has been predicted to be independent of the size of
the system. Furthermore, it has been predicted that the ground state energy
E(N) of the N-atom system varies exponentially as the atomic mass approaches
m*. This paper reports accurate numerical many-body calculations that allow
these predictions to be tested. We confirm the existence of a universal
critical mass m*, and show that the near-threshold behavior can only be
described properly if a previously neglected term is included. We comment on
the universality of the energy ratio E(N+1)/E(N) near threshold.Comment: 6 pages, 3 figure
Quarkonia Measurements with the Central Detectors of ALICE
A Large Ion Collider Experiment - ALICE will become operational with the
startup of the Large Hadron Collider - LHC at the end of 2007. One focus of the
physics program is the measurement of quarkonia in proton-proton and lead-lead
collisions. Quarkonia states will be measured in two kinematic regions and
channels: di-muonic decays will be measured in the forward region by the muon
arm, the central part of the detector will measure di-electronic decays. The
presented studies show the expected performance of the di-electron measurement
in proton-proton and central lead-lead collisions.Comment: 6 pages, 7 figures, Proceedings of the QM 2006 poster sessio
The Trapped Polarized Fermi Gas at Unitarity
We consider population-imbalanced two-component Fermi gases under external
harmonic confinement interacting through short-range two-body potentials with
diverging s-wave scattering length. Using the fixed-node diffusion Monte Carlo
method, the energies of the "normal state" are determined as functions of the
population-imbalance and the number of particles. The energies of the trapped
system follow, to a good approximation, a universal curve even for fairly small
systems. A simple parameterization of the universal curve is presented and
related to the equation of state of the bulk system.Comment: 4 pages, 2 tables, 2 figure
Development of UHF radiometer
A wideband multifrequency UHF radiometer was initially developed to operate in the 500 to 710 MHz frequency range for the remote measurement of ocean water salinity. However, radio-frequency interference required a reconfiguration to operate in the single-frequency radio astronomy band of 608 to 614 MHz. Details of the radiometer development and testing are described. Flight testing over variable terrain provided a performance comparison of the UHF radiometer with an L-band radiometer for remote sensing of geophysical parameters. Although theoretically more sensitive, the UHF radiometer was found to be less desirable in practice than the L-band radiometer
Dilute Bose gases interacting via power-law potentials
Neutral atoms interact through a van der Waals potential which asymptotically
falls off as r^{-6}. In ultracold gases, this interaction can be described to a
good approximation by the atom-atom scattering length. However, corrections
arise that depend on the characteristic length of the van der Waals potential.
We parameterize these corrections by analyzing the energies of two- and
few-atom systems under external harmonic confinement, obtained by numerically
and analytically solving the Schrodinger equation. We generalize our results to
particles interacting through a longer-ranged potential which asymptotically
falls off as r^{-4}.Comment: 7 pages, 4 figure
Dipolar Bose gases: Many-body versus mean-field description
We characterize zero-temperature dipolar Bose gases under external spherical
confinement as a function of the dipole strength using the essentially exact
many-body diffusion Monte Carlo (DMC) technique. We show that the DMC energies
are reproduced accurately within a mean-field framework if the variation of the
s-wave scattering length with the dipole strength is accounted for properly.
Our calculations suggest stability diagrams and collapse mechanisms of dipolar
Bose gases that differ significantly from those previously proposed in the
literature
Quasi-one-dimensional Bose gases with large scattering length
Bose gases confined in highly-elongated harmonic traps are investigated over
a wide range of interaction strengths using quantum Monte Carlo techniques. We
find that the properties of a Bose gas under tight transverse confinement are
well reproduced by a 1d model Hamiltonian with contact interactions. We point
out the existence of a unitary regime, where the properties of the quasi-1d
Bose gas become independent of the actual value of the 3d scattering length. In
this unitary regime, the energy of the system is well described by a hard rod
equation of state. We investigate the stability of quasi-1d Bose gases with
positive and negative 3d scattering length.Comment: 5 pages, 3 figure
Feshbach Resonance Cooling of Trapped Atom Pairs
Spectroscopic studies of few-body systems at ultracold temperatures provide
valuable information that often cannot be extracted in a hot environment.
Considering a pair of atoms, we propose a cooling mechanism that makes use of a
scattering Feshbach resonance. Application of a series of time-dependent
magnetic field ramps results in the situation in which either zero, one, or two
atoms remain trapped. If two atoms remain in the trap after the field ramps are
completed, then they have been cooled. Application of the proposed cooling
mechanism to optical traps or lattices is considered.Comment: 5 pages, 3 figures; v.2: major conceptual change
Quantum fluctuation induced ordered phase in the Blume-Capel model
We consider the Blume-Capel model with the quantum tunneling between the
excited states. We find a magnetically ordered phase transition induced by
quantum fluctuation in a model. The model has no phase transition in the
corresponding classical case. Usually, quantum fluctuation breaks ordered phase
as in the case of the transverse field Ising model. However, in present case,
an ordered phase is induced by quantum fluctuation. Moreover, we find a phase
transition between a quantum paramagnetic phase and a classical diamagnetic
phase at zero temperature. We study the properties of the phase transition by
using a mean field approximation (MFA), and then, by a quantum Monte Carlo
method to confirm the result of the MFA.Comment: 7 pages, 6 figures, corrected some typo
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