38,208 research outputs found
A comprehensive treatment of electromagnetic interactions and the three-body spectator equations
We present a general derivation the three-body spectator (Gross) equations
and the corresponding electromagnetic currents. As in previous paper on
two-body systems, the wave equations and currents are derived from those for
Bethe-Salpeter equation with the help of algebraic method using a concise
matrix notation. The three-body interactions and currents introduced by the
transition to the spectator approach are isolated and the matrix elements of
the e.m. current are presented in detail for system of three indistinguishable
particles, namely for elastic scattering and for two and three body break-up.
The general expressions are reduced to the one-boson-exchange approximation to
make contact with previous work. The method is general in that it does not rely
on introduction of the electromagnetic interaction with the help of the minimal
replacement. It would therefore work also for other external fields
More on Phase Structure of Nonlocal 2D Generalized Yang-Mills Theories (nlgYM's)
We study the phase structure of nonlocal two dimensional generalized Yang -
Mills theories (nlgYM) and it is shown that all order of model
of these theories has phase transition only on compact manifold with (on
sphere), and the order of phase transition is 3. Also it is shown that the
model of nlgYM has third order phase
transition on any compact manifold with ,
and has no phase transition on sphere.Comment: 11 pages, no figure
Novel schemes for measurement-based quantum computation
We establish a framework which allows one to construct novel schemes for
measurement-based quantum computation. The technique further develops tools
from many-body physics - based on finitely correlated or projected entangled
pair states - to go beyond the cluster-state based one-way computer. We
identify resource states that are radically different from the cluster state,
in that they exhibit non-vanishing correlation functions, can partly be
prepared using gates with non-maximal entangling power, or have very different
local entanglement properties. In the computational models, the randomness is
compensated in a different manner. It is shown that there exist resource states
which are locally arbitrarily close to a pure state. Finally, we comment on the
possibility of tailoring computational models to specific physical systems as,
e.g. cold atoms in optical lattices.Comment: 5 pages RevTeX, 1 figure, many diagrams. Title changed, presentation
improved, material adde
Supersonic quantum communication
When locally exciting a quantum lattice model, the excitation will propagate
through the lattice. The effect is responsible for a wealth of non-equilibrium
phenomena, and has been exploited to transmit quantum information through spin
chains. It is a commonly expressed belief that for local Hamiltonians, any such
propagation happens at a finite "speed of sound". Indeed, the Lieb-Robinson
theorem states that in spin models, all effects caused by a perturbation are
limited to a causal cone defined by a constant speed, up to exponentially small
corrections. In this work we show that for translationally invariant bosonic
models with nearest-neighbor interactions, this belief is incorrect: We prove
that one can encounter excitations which accelerate under the natural dynamics
of the lattice and allow for reliable transmission of information faster than
any finite speed of sound. The effect is only limited by the model's range of
validity (eventually by relativity). It also implies that in non-equilibrium
dynamics of strongly correlated bosonic models far-away regions may become
quickly entangled, suggesting that their simulation may be much harder than
that of spin chains even in the low energy sector.Comment: 4+3 pages, 1 figure, some material added, typographic error fixe
From Surface Operators to Non-Abelian Volume Operators in Puff Field Theory
Puff Field Theory is a low energy decoupling regime of string theory that
still retains the non-local attributes of the parent theory - while preserving
isotropy for its non-local degrees of freedom. It realizes an extended
holographic dictionary at strong coupling and dynamical non-local states akin
to defects or the surface operators of local gauge theories. In this work, we
probe the non-local features of PFT using D3 branes. We find supersymmetric
configurations that end on defects endowed with non-Abelian degrees of freedom.
These are 2+1 dimensional defects in the 3+1 dimensional PFT that may be viewed
as volume operators. We determine their R-charge, vacuum expectation value,
energy, and gauge group structure.Comment: 39 pages, 6 figure
Enumerative aspects of the Gross-Siebert program
We present enumerative aspects of the Gross-Siebert program in this
introductory survey. After sketching the program's main themes and goals, we
review the basic definitions and results of logarithmic and tropical geometry.
We give examples and a proof for counting algebraic curves via tropical curves.
To illustrate an application of tropical geometry and the Gross-Siebert program
to mirror symmetry, we discuss the mirror symmetry of the projective plane.Comment: A version of these notes will appear as a chapter in an upcoming
Fields Institute volume. 81 page
Measuring and engineering entropy and spin squeezing in weakly linked Bose-Einstein condensates
We propose a method to infer the single-particle entropy of bosonic atoms in
an optical lattice and to study the local evolution of entropy, spin squeezing,
and entropic inequalities for entanglement detection in such systems. This
method is based on experimentally feasible measurements of
non-nearest-neighbour coherences. We study a specific example of dynamically
controlling atom tunneling between selected sites and show that this could
potentially also improve the metrologically relevant spin squeezing
Confinement and the analytic structure of the one body propagator in Scalar QED
We investigate the behavior of the one body propagator in SQED. The self
energy is calculated using three different methods: i) the simple bubble
summation, ii) the Dyson-Schwinger equation, and iii) the Feynman-Schwinger
represantation. The Feynman-Schwinger representation allows an {\em exact}
analytical result. It is shown that, while the exact result produces a real
mass pole for all couplings, the bubble sum and the Dyson-Schwinger approach in
rainbow approximation leads to complex mass poles beyond a certain critical
coupling. The model exhibits confinement, yet the exact solution still has one
body propagators with {\it real} mass poles.Comment: 5 pages 2 figures, accepted for publication in Phys. Rev.
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