3,443 research outputs found
Dual Methods for Lattice Field Theories at Finite Density
We present a dual representation of the partition function of the charged
scalar field in which the complex action problem at non-zero chemical potential
is absent. In this dual representation Monte Carlo simulations are possible and
we show some physical results obtained with this approach. Furthermore we
present a technique to study 2-point functions at finite density. Results for
the lattice correlators at various chemical potentials are shown and discussed.Comment: 7 pages, 2 figures, presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Solving the sign problems of the massless lattice Schwinger model with a dual formulation
We derive an exact representation of the massless Schwinger model on the
lattice in terms of dual variables which are configurations of loops, dimers
and plaquette occupation numbers. When expressed with the dual variables the
partition sum has only real and positive terms also when a chemical potential
or a topological term are added -- situations where the conventional
representation has a complex action problem. The dual representation allows for
Monte Carlo simulations without restrictions on the values of the chemical
potential or the vacuum angle.Comment: Several comments added. Final version to appear in Nuclear Physics
Transforming structures by set interpretations
We consider a new kind of interpretation over relational structures: finite
sets interpretations. Those interpretations are defined by weak monadic
second-order (WMSO) formulas with free set variables. They transform a given
structure into a structure with a domain consisting of finite sets of elements
of the orignal structure. The definition of these interpretations directly
implies that they send structures with a decidable WMSO theory to structures
with a decidable first-order theory. In this paper, we investigate the
expressive power of such interpretations applied to infinite deterministic
trees. The results can be used in the study of automatic and tree-automatic
structures.Comment: 36 page
Shaping frequency entangled qudits
Quantum entanglement between qudits - the d-dimensional version of qubits -
is relevant for advanced quantum information processing and provides deeper
insights in the nature of quantum correlations. Encoding qudits in the
frequency modes of photon pairs produced by continuous parametric
down-conversion enables access to high-dimensional states. By shaping the
energy spectrum of entangled photons, we demonstrate the creation,
characterization and manipulation of entangled qudits with dimension up to 4.
Their respective density matrices are reconstructed by quantum state
tomography. For qubits and qutrits we additionally measured the dependency of a
d-dimensional Bell parameter for various degrees of entanglement. Our
experiment demonstrates the ability to investigate the physics of
high-dimensional frequency entangled quit states which are of great
importance for quantum information science.Comment: 17 pages, 3 figure
Versatile shaper-assisted discretization of energy-time entangled photons
We demonstrate the capability to discretize the frequency spectrum of
broadband energy-time entangled photons by means of a spatial light modulator
to encode qudits in various bases. Exemplarily, we implement three different
discretization schemes, namely frequency bins, time bins and Schmidt modes.
Entangled qudits up to dimension are then revealed by two-photon
interference experiments with visibilities violating a -dimensional Bell
inequality.Comment: 22 pages, 11 figure
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