9,714 research outputs found
A generalized structure of Bell inequalities for bipartite arbitrary dimensional systems
We propose a generalized structure of Bell inequalities for arbitrary
d-dimensional bipartite systems, which includes the existing two types of Bell
inequalities introduced by Collins-Gisin-Linden-Massar-Popescu [Phys. Rev.
Lett. 88, 040404 (2002)] and Son-Lee-Kim [Phys. Rev. Lett. 96, 060406 (2006)].
We analyze Bell inequalities in terms of correlation functions and joint
probabilities, and show that the coefficients of correlation functions and
those of joint probabilities are in Fourier transform relations. We finally
show that the coefficients in the generalized structure determine the
characteristics of quantum violation and tightness.Comment: 6 pages, 1 figur
Disordered Quantum Spin Chains with Long-Range Antiferromagnetic Interactions
We investigate the magnetic susceptibility of quantum spin chains
of spins with power-law long-range antiferromagnetic coupling as a
function of their spatial decay exponent and cutoff length . The
calculations are based on the strong disorder renormalization method which is
used to obtain the temperature dependence of and distribution
functions of couplings at each renormalization step. For the case with only
algebraic decay () we find a crossover at
between a phase with a divergent low-temperature susceptibility
for to a phase with a vanishing
for . For finite cutoff lengths
, this crossover occurs at a smaller . Additionally we
study the localization of spin excitations for by evaluating
the distribution function of excitation energies and we find a delocalization
transition that coincides with the opening of the pseudo-gap at
.Comment: 6 pages, 7 figure
Near-Complete Teleportation of a Superposed Coherent State
The four Bell-type entangled coherent states, |\alpha>|-\alpha> \pm |-\alpha>
|\alpha> and |\alpha>|\alpha> \pm |-\alpha> |-\alpha>, can be discriminated
with a high probability using only linear optical means, as long as |\alpha| is
not too small. Based on this observation, we propose a simple scheme to almost
completely teleport a superposed coherent state. The nonunitary transformation,
that is required to complete the teleportation, can be achieved by embedding
the receiver's field state in a larger Hilbert space consisting of the field
and a single atom and performing a unitary transformation on this Hilbert
space.Comment: 4 pages,3 figures, Two columns, LaTex2
Dyon condensation in topological Mott insulators
We consider quantum phase transitions out of topological Mott insulators in
which the ground state of the fractionalized excitations (fermionic spinons) is
topologically non-trivial. The spinons in topological Mott insulators are
coupled to an emergent compact U(1) gauge field with a so-called "axion" term.
We study the confinement transitions from the topological Mott insulator to
broken symmetry phases, which may occur via the condensation of dyons. Dyons
carry both "electric" and "magnetic" charges, and arise naturally in this
system because the monopoles of the emergent U(1) gauge theory acquires gauge
charge due to the axion term. It is shown that the dyon condensate, in general,
induces simultaneous current and bond orders. To demonstrate this, we study the
confined phase of the topological Mott insulator on the cubic lattice. When the
magnetic transition is driven by dyon condensation, we identify the bond order
as valence bond solid order and the current order as scalar spin chirality
order. Hence, the confined phase of the topological Mott insulator is an exotic
phase where the scalar spin chirality and the valence bond order coexist and
appear via a single transition. We discuss implications of our results for
generic models of topological Mott insulators.Comment: 14 pages, accepted to the New Journal of Physic
Identifying First-person Camera Wearers in Third-person Videos
We consider scenarios in which we wish to perform joint scene understanding,
object tracking, activity recognition, and other tasks in environments in which
multiple people are wearing body-worn cameras while a third-person static
camera also captures the scene. To do this, we need to establish person-level
correspondences across first- and third-person videos, which is challenging
because the camera wearer is not visible from his/her own egocentric video,
preventing the use of direct feature matching. In this paper, we propose a new
semi-Siamese Convolutional Neural Network architecture to address this novel
challenge. We formulate the problem as learning a joint embedding space for
first- and third-person videos that considers both spatial- and motion-domain
cues. A new triplet loss function is designed to minimize the distance between
correct first- and third-person matches while maximizing the distance between
incorrect ones. This end-to-end approach performs significantly better than
several baselines, in part by learning the first- and third-person features
optimized for matching jointly with the distance measure itself
Robustness of multiparty nonlocality to local decoherence
We investigate the robustness of multiparty nonlocality under local
decoherence, acting independently and equally on each subsystems. To be
specific, we consider an N-qubit GHZ state under depolarization, dephasing, or
dissipation channel, and tested the nonlocality by violation of Mermin-Klyshko
inequality, which is one of Bell's inequalities for multi-qubit systems. The
results show that the robustness of nonlocality increases with the number of
qubits, and that the nonlocality of an N-qubit GHZ state with even N is
extremely persistent against dephasing.Comment: 5 pages, 4 figure
The role of Causality in Tunable Fermi Gas Condensates
We develop a new formalism for the description of the condensates of cold
Fermi atoms whose speed of sound can be tuned with the aid of a narrow Feshbach
resonance. We use this to look for spontaneous phonon creation that mimics
spontaneous particle creation in curved space-time in
Friedmann-Robertson-Walker and other model universes.Comment: 9 pages, 2 figures. In v.3 the formalism is different from the
existing arXiv versions, but the final results are unchanged. Title changed,
one author added. The article will be published in the special edition of
Journal of Physics: Condensed Matter on "Condensed matter analogues of
cosmology
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