18 research outputs found
Development of Grid e-Infrastructure in South-Eastern Europe
Over the period of 6 years and three phases, the SEE-GRID programme has
established a strong regional human network in the area of distributed
scientific computing and has set up a powerful regional Grid infrastructure. It
attracted a number of user communities and applications from diverse fields
from countries throughout the South-Eastern Europe. From the infrastructure
point view, the first project phase has established a pilot Grid infrastructure
with more than 20 resource centers in 11 countries. During the subsequent two
phases of the project, the infrastructure has grown to currently 55 resource
centers with more than 6600 CPUs and 750 TBs of disk storage, distributed in 16
participating countries. Inclusion of new resource centers to the existing
infrastructure, as well as a support to new user communities, has demanded
setup of regionally distributed core services, development of new monitoring
and operational tools, and close collaboration of all partner institution in
managing such a complex infrastructure. In this paper we give an overview of
the development and current status of SEE-GRID regional infrastructure and
describe its transition to the NGI-based Grid model in EGI, with the strong SEE
regional collaboration.Comment: 22 pages, 12 figures, 4 table
Topological d-wave pairing structures in Jain states
We discuss d-wave topological (broken time reversal symmetry) pairing
structures in unpolarized and polarized Jain states. We demonstrate pairing in
the Jain spin singlet state by rewriting it in an explicit pairing form, in
which we can recognize d-wave weak pairing of underlying quasiparticles -
neutral fermions. We find and describe the root configuration of the Jain spin
singlet state and its connection with neutral excitations of the Haldane-Rezayi
state, and study the transition between these states via exact diagonalization.
We find high overlaps with the Jain spin singlet state upon a departure from
the hollow core model for which the Haldane-Rezayi state is the exact ground
state. Due to a proven algebraic identity we were able to extend the analysis
of topological d-wave pairing structures to polarized Jain states and integer
quantum Hall states, and discuss its consequences.Comment: 8 page
Geometric Resonances in Bose-Einstein Condensates with Two- and Three-Body Interactions
We investigate geometric resonances in Bose-Einstein condensates by solving
the underlying time-dependent Gross-Pitaevskii equation for systems with two-
and three-body interactions in an axially-symmetric harmonic trap. To this end,
we use a recently developed analytical method [Phys. Rev. A 84, 013618 (2011)],
based on both a perturbative expansion and a Poincar\'e-Lindstedt analysis of a
Gaussian variational approach, as well as a detailed numerical study of a set
of ordinary differential equations for variational parameters. By changing the
anisotropy of the confining potential, we numerically observe and analytically
describe strong nonlinear effects: shifts in the frequencies and mode coupling
of collective modes, as well as resonances. Furthermore, we discuss in detail
the stability of a Bose-Einstein condensate in the presence of an attractive
two-body interaction and a repulsive three-body interaction. In particular, we
show that a small repulsive three-body interaction is able to significantly
extend the stability region of the condensate.Comment: 27 pages, 13 figure
Fast Convergence of Path Integrals for Many-body Systems
We generalize a recently developed method for accelerated Monte Carlo
calculation of path integrals to the physically relevant case of generic
many-body systems. This is done by developing an analytic procedure for
constructing a hierarchy of effective actions leading to improvements in
convergence of -fold discretized many-body path integral expressions from
1/N to for generic . In this paper we present explicit solutions
within this hierarchy up to level . Using this we calculate the low lying
energy levels of a two particle model with quartic interactions for several
values of coupling and demonstrate agreement with analytical results governing
the increase in efficiency of the new method. The applicability of the
developed scheme is further extended to the calculation of energy expectation
values through the construction of associated energy estimators exhibiting the
same speedup in convergence.Comment: 20 pages, 6 figures, 1 tabl
Modified Coulomb gas construction of quantum Hall states from non-unitary conformal field theories
15 pages, published version, improved redactionInternational audienceSome fractional quantum Hall states observed in experiments may be described by first-quantized wavefunctions with special clustering properties like the Moore-Read Pfaffian for filling factor nu = 5/2. This wavefunction has been constructed by constructing correlation functions of a two-dimensional conformal field theory (CFT) involving a free boson and a Majorana fermion. By considering other CFTs many other clustered states have been proposed as candidate FQH states under appropriate circumstances. It is believed that the underlying CFT should be unitary if one wants to describe an incompressible i.e. gapped liquid state. We show that by changing the way one derives the wavefunction from its parent CFT it is possible to obtain an incompressible candidate state when starting from a non-unitary parent. The construction mimics a global change of parameters in the phase space of the electron system. We explicit our construction in the case of the so-called Gaffnian state (a state for filling factor 2/5) and also for the Haldane-Rezayi state (a spin-singlet state at filling 1/2)