12,630 research outputs found
Quark fragmentation in the -vacuum
The vacuum of Quantum Chromodynamics is a superposition of degenerate states
with different topological numbers that are connected by tunneling (the
-vacuum). The tunneling events are due to topologically non-trivial
configurations of gauge fields (e.g. the instantons) that induce local \p-odd
domains in Minkowski space-time. We study the quark fragmentation in this
topologically non-trivial QCD background. We find that even though QCD globally
conserves \p and \cp symmetries, two new kinds of \p-odd fragmentation
functions emerge. They generate interesting dihadron correlations: one is the
azimuthal angle correlation usually referred to as
the Collins effect, and the other is the \p-odd correlation that vanishes in the cross section summed over many events, but
survives on the event-by-event basis. Using the chiral quark model we estimate
the magnitude of these new fragmentation functions. We study their experimental
manifestations in dihadron production in collisions, and comment on
the applicability of our approach in deep-inelastic scattering, proton-proton
and heavy ion collisions.Comment: 4 pages, 2 figure
Realization of random-field dipolar Ising ferromagnetism in a molecular magnet
The longitudinal magnetic susceptibility of single crystals of the molecular
magnet Mn-acetate obeys a Curie-Weiss law, indicating a transition to a
ferromagnetic phase due to dipolar interactions. With increasing magnetic field
applied transverse to the easy axis, the transition temperature decreases
considerably more rapidly than predicted by mean field theory to a T=0 quantum
critical point. Our results are consistent with an effective Hamiltonian for a
random-field Ising ferromagnet in a transverse field, where the randomness is
induced by an external field applied to Mn-acetate crystals that are
known to have an intrinsic distribution of locally tilted magnetic easy axes.Comment: 4 pages, 4 figure
Pair Distribution Function of One-dimensional "Hard Sphere" Fermi and Bose Systems
The pair distributions of one-dimensional "hard sphere" fermion and boson
systems are exactly evaluated by introducing gap variables.Comment: 4 page
Magnetic noise around metallic microstructures
We compute the local spectrum of the magnetic field near a metallic
microstructure at finite temperature. Our main focus is on deviations from a
plane-layered geometry for which we review the main properties. Arbitrary
geometries are handled with the help of numerical calculations based on surface
integral equations. The magnetic noise shows a significant polarization
anisotropy above flat wires with finite lateral width, in stark contrast to an
infinitely wide wire. Within the limits of a two-dimensional setting, our
results provide accurate estimates for loss and dephasing rates in so-called
`atom chip traps' based on metallic wires. A simple approximation based on the
incoherent summation of local current elements gives qualitative agreement with
the numerics, but fails to describe current correlations among neighboring
objects.Comment: 10 pages, 9 figures, accepted for publication in J Appl Phys; figures
plotted for slightly smaller structur
Experimental determination of the Weiss temperature of Mn-ac and Mn-ac-MeOH
We report measurements of the susceptibility in the temperature range from
K to K of a series of Mn-ac and Mn-ac-MeOH samples in
the shape of rectangular prisms of length and square cross-section of
side . The susceptibility obeys a Curie-Weiss Law, ,
where varies systematically with sample aspect ratio. Using published
demagnetization factors, we obtain for an infinitely long sample
corresponding to intrinsic ordering temperatures K and
K for Mn-ac and Mn-ac-MeOH, respectively. The
difference in for two materials that have nearly identical unit cell
volumes and lattice constant ratios suggests that, in addition to dipolar
interactions, there is a non-dipolar (exchange) contribution to the Weiss
temperature that differs in the two materials because of the difference in
ligand molecules.Comment: 4.5 page
Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate
We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein
condensate by a temporal modulation of spin exchange interaction, which is
tunable with optical Feshbach resonance. Adopting techniques from coherent
control, we demonstrate the localization/freezing of spin mixing dynamics, and
the suppression of the intrinsic dynamic instability and spontaneous spin
domain formation in a ferromagnetically interacting condensate of Rb
atoms. This work points to a promising scheme for investigating the weak
magnetic spin dipole interaction, which is usually masked by the more dominant
spin exchange interaction.Comment: 4 pages, 5 eps figures, published in Phys. Rev. A
Nonclassicality of quantum excitation of classical coherent field in photon loss channel
We investigate the nonclassicality of photon-added coherent states in the
photon loss channel by exploring the entanglement potential and negative Wigner
distribution. The total negative probability defined by the absolute value of
the integral of the Wigner function over the negative distribution region
reduces with the increase of decay time. The total negative probability and the
entanglement potential of pure photon-added coherent states exhibit the similar
dependence on the beam intensity. The reduce of the total negative probability
is consistent with the behavior of entanglement potential for the dissipative
single-photon-added coherent state at short decay times.Comment: 5 pages, 5 figures, RevTex4, submitte
Linear optical quantum computation with imperfect entangled photon-pair sources and inefficient non-photon-number-resolving detectors
We propose a scheme for efficient cluster state quantum computation by using
imperfect polarization-entangled photon-pair sources, linear optical elements
and inefficient non-photon-number-resolving detectors. The efficiency threshold
for loss tolerance in our scheme requires the product of source and detector
efficiencies should be >1/2 - the best known figure. This figure applies to
uncorrelated loss. We further find that the loss threshold is unaffected by
correlated loss in the photon pair source. Our approach sheds new light on
efficient linear optical quantum computation with imperfect experimental
conditions.Comment: 5 pages, 2 figure
Identifying strongly correlated supersolid states on the optical lattice by quench-induced \pi-states
We consider the rapid quench of a one-dimensional strongly correlated
supersolid to a localized density wave (checkerboard) phase, and calculate the
first-order coherence signal following the quench. It is shown that unique
coherence oscillations between the even and odd sublattice sites of the
checkerboard are created by the quench, which are absent when the initial state
is described by a Gutzwiller product state. This is a striking manifestation of
the versatility of the far-from-equilbrium and nonperturbative collapse and
revival phenomenon as a microscope for quantum correlations in complex
many-body states. For the present example, this opens up the possibility to
discriminate experimentally between mean-field and many-body origins of
supersolidity.Comment: 6 pages of EPL2 style, 5 figure
Non-Perturbative Theory of Dispersion Interactions
Some open questions exist with fluctuation-induced forces between extended
dipoles. Conventional intuition derives from large-separation perturbative
approximations to dispersion force theory. Here we present a full
non-perturbative theory. In addition we discuss how one can take into account
finite dipole size corrections. It is of fundamental value to investigate the
limits of validity of the perturbative dispersion force theory.Comment: 9 pages, no figure
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