29,524 research outputs found
Observation of valley Landau-Zener-Bloch oscillations and pseudospin imbalance in photonic graphene
We demonstrate inter-valley Bloch oscillation (BO) and Landau-Zener tunneling
(LZT) in an optically-induced honeycomb lattice with a refractive index
gradient. Unlike previously observed BO in a gapped square lattice, we show
non-adiabatic beam dynamics that are highly sensitive to the direction of the
index gradient and the choice of the Dirac cones. In particular, a
symmetry-preserving potential leads to nearly perfect LZT and coherent BO
between the inequivalent valleys, whereas a symmetry-breaking potential
generates asymmetric scattering, imperfect LZT, and valley-sensitive generation
of vortices mediated by a pseudospin imbalance. This clearly indicates that,
near the Dirac points, the transverse gradient does not always act as a simple
scalar force as commonly assumed, and the LZT probability is strongly affected
by the sublattice symmetry as analyzed from an effective Landau-Zener
Hamiltonian. Our results illustrate the anisotropic response of an otherwise
isotropic Dirac platform to real-space potentials acting as strong driving
fields, which may be useful for manipulation of pseudospin and valley degrees
of freedom in graphene-like systems
Kaon and pion parton distribution amplitudes to twist-three
We compute all kaon and pion parton distribution amplitudes (PDAs) to
twist-three and find that only the pseudotensor PDA can reasonably be
approximated by its conformal limit expression. At terrestrially accessible
energy scales, the twist-two and pseudoscalar twist-three PDAs differ
significantly from those functions commonly associated with their forms in
QCD's conformal limit. In all amplitudes studied, SU(3) flavour-symmetry
breaking is typically a 13% effect. This scale is determined by nonperturbative
dynamics; namely, the current-quark-mass dependence of dynamical chiral
symmetry breaking. The heavier-quark is favoured by this distortion, for
example, support is shifted to the s-quark in the negative kaon. It appears,
therefore, that at energy scales accessible with existing and foreseeable
facilities, one may obtain reliable expectations for experimental outcomes by
using these "strongly dressed" PDAs in formulae for hard exclusive processes.
Following this procedure, any discrepancies between experiment and theory will
be significantly smaller than those produced by using the conformal-limit PDAs.
Moreover, the magnitude of any disagreement will either be a better estimate of
higher-order, higher-twist effects or provide more realistic constraints on the
Standard Model.Comment: 14 pages, 4 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1406.335
Bond distortion effects and electric orders in spiral multiferroic magnets
We study in this paper bond distortion effect on electric polarization in
spiral multiferroic magnets based on cluster and chain models. The bond
distortion break inversion symmetry and modify the - hybridization.
Consequently, it will affect electric polarization which can be divided into
spin-current part and lattice-mediated part. The spin-current polarization can
be written in terms of and
the lattice-mediated polarization exists only when the M-O-M bond is distorted.
The electric polarization for three-atom M-O-M and four-atom M-O-M
clusters is calculated. We also study possible electric ordering in three kinds
of chains made of different clusters. We apply our theory to multiferroics
cuprates and find that the results are in agreement with experimental
observations.Comment: 14 pages, 11 figure
Teleportation of an arbitrary multipartite state via photonic Faraday rotation
We propose a practical scheme for deterministically teleporting an arbitrary
multipartite state, either product or entangled, using Faraday rotation of the
photonic polarization. Our scheme, based on the input-output process of
single-photon pulses regarding cavities, works in low-Q cavities and only
involves virtual excitation of the atoms, which is insensitive to both cavity
decay and atomic spontaneous emission. Besides, the Bell-state measurement is
accomplished by the Faraday rotation plus product-state measurements, which
could much relax the experimental difficulty to realize the Bell-state
measurement by the CNOT operation.Comment: 11 pages, 2 figures
Theory of the Three-Group Evolutionary Minority Game
Based on the adiabatic theory for the evolutionary minority game (EMG) that
we proposed earlier[1], we perform a detail analysis of the EMG limited to
three groups of agents. We derive a formula for the critical point of the
transition from segregation (into opposing groups) to clustering (towards
cautious behaviors). Particular to the three-group EMG, the strategy switching
in the "extreme" group does not occur at every losing step and is strongly
intermittent. This leads to an correction to the critical value of the number
of agents at the transition, . Our expression for is in agreement
with the results obtained from our numerical simulations.Comment: 4 pages and 2 figure
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