101,643 research outputs found
Quantum phases of a Feshbach-resonant atomic Bose gas in one dimension
We study an atomic Bose gas with an s-wave Feshbach resonance in a
one-dimensional optical lattice, with the densities of atoms and molecules
incommensurate with the lattice. At zero temperature, most of the parameter
region is occupied by a phase in which the superfluid fluctuations of atoms and
molecules are the predominant ones, due to the phase fluctuations of atoms and
molecules being locked by a Josephson coupling between them. When the density
difference between atoms and molecules is commensurate with the lattice, two
additional phases may exist: the two component Luttinger liquid where both the
atomic and molecular sectors are gapless, and the inter-channel charge density
wave where the relative density fluctuations between atoms and molecules are
frozen at low energy.Comment: 4+epsilon pages, 3 figures; references adde
Optical Spatial integration methods for ambiguity function generation
A coherent optical spatial integration approach to ambiguity function generation is described. It uses one dimensional acousto-optic Bragg cells as input tranducers in conjunction with a space variant linear phase shifter, a passive optical element, to generate the two dimensional ambiguity function in one exposure. Results of a real time implementation of this system are shown
Observation of Scalar Aharonov-Bohm Effect with Longitudinally Polarized Neutrons
We have carried out a neutron interferometry experiment using longitudinally polarized neutrons to observe the scalar Aharonov-Bohm effect. The neutrons inside the interferometer are polarized parallel to an applied pulsed magnetic field B(t). The pulsed B field is spatially uniform so it exerts no force on the neutrons. Its direction also precludes the presence of any classical torque to change the neutron polarization
Scalar Aharonov-Bohm effect with longitudinally polarized neutrons
In the scalar Aharonov-Bohm effect, a charged particle (electron) interacts with the scalar electrostatic potential U in the field-free (i.e., force-free) region inside an electrostatic cylinder (Faraday cage). Using a perfect single-crystal neutron interferometer we have performed a “dual” scalar Aharonov-Bohm experiment by subjecting polarized thermal neutrons to a pulsed magnetic field. The pulsed magnetic field was spatially uniform, precluding any force on the neutrons. Aligning the direction of the pulsed magnetic field to the neutron magnetic moment also rules out any classical torque acting to change the neutron polarization. The observed phase shift is purely quantum mechanical in origin. A detailed description of the experiment, performed at the University of Missouri Research Reactor, and its interpretation is given in this paper
Magnetic switching by spin torque from the spin Hall effect
The spin Hall effect (SHE) generates spin currents within nonmagnetic
materials. Previously, studies of the SHE have been motivated primarily to
understand its fundamental origin and magnitude. Here we demonstrate, using
measurement and modeling, that in a Pt/Co bilayer with perpendicular magnetic
anisotropy the SHE can produce a spin transfer torque that is strong enough to
efficiently rotate and reversibly switch the Co magnetization, thereby
providing a new strategy both to understand the SHE and to manipulate magnets.
We suggest that the SHE torque can have a similarly strong influence on
current-driven magnetic domain wall motion in Pt/ferromagnet multilayers. We
estimate that in optimized devices the SHE torque can switch magnetic moments
using currents comparable to those in magnetic tunnel junctions operated by
conventional spin-torque switching, meaning that the SHE can enable magnetic
memory and logic devices with similar performance but simpler architecture than
the current state of the art
Weighted feature selection criteria for visual servoing of a telerobot
Because of the continually changing environment of a space station, visual feedback is a vital element of a telerobotic system. A real time visual servoing system would allow a telerobot to track and manipulate randomly moving objects. Methodologies for the automatic selection of image features to be used to visually control the relative position between an eye-in-hand telerobot and a known object are devised. A weighted criteria function with both image recognition and control components is used to select the combination of image features which provides the best control. Simulation and experimental results of a PUMA robot arm visually tracking a randomly moving carburetor gasket with a visual update time of 70 milliseconds are discussed
A Solvable Model for Many Quark Systems in QCD Hamiltonians
Motivated by a canonical, QCD Hamiltonian we propose an effective Hamiltonian
to represent an arbitrary number of quarks in hadronic bags. The structure of
the effective Hamiltonian is discussed and the BCS-type solutions that may
represent constituent quarks are presented. The single particle orbitals are
chosen as 3-dimensional harmonic oscillators and we discuss a class of exact
solutions that can be obtained when a subset of single-particle basis states is
restricted to include a certain number of orbital excitations. The general
problem, which includes all possible orbital states, can also be solved by
combining analytical and numerical methods.Comment: 24 pages, 2 figures, research articl
Phase diagram of the three band half-filled Cu-O two-leg ladder
We determine the phase diagram of the half-filled two-leg ladder both at weak
and strong coupling, taking into account the Cu d_{x^2-y^2} and the O p_x and
p_y orbitals. At weak coupling, renormalization group flows are interpreted
with the use of bosonization. Two different models with and without outer
oxygen orbitals are examined. For physical parameters, and in the absence of
the outer oxygen orbitals, the D-Mott phase arises; a dimerized phase appears
when the outer oxygen atoms are included. We show that the circulating current
phase that preserves translational symmetry does not appear at weak coupling.
In the opposite strong-coupling atomic limit the model is purely electrostatic
and the ground states may be found by simple energy minimization. The phase
diagram so obtained is compared to the weak-coupling one.Comment: 10 pages, 5 figures, Version accepted for publication in PR
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