173 research outputs found
Ground-State Fidelity and Bipartite Entanglement in the Bose-Hubbard Model
We analyze the quantum phase transition in the Bose-Hubbard model borrowing
two tools from quantum-information theory, i.e. the ground-state fidelity and
entanglement measures. We consider systems at unitary filling comprising up to
50 sites and show for the first time that a finite-size scaling analysis of
these quantities provides excellent estimates for the quantum critical point.We
conclude that fidelity is particularly suited for revealing a quantum phase
transition and pinning down the critical point thereof, while the success of
entanglement measures depends on the mechanisms governing the transition.Comment: 7 pages, 5 figures (endfloats used due to problems with figures and
latex. Sorry about that); final version, similar to the published on
Phase diagram of the bose Hubbard model
The first reliable analytic calculation of the phase diagram of the bose gas
on a -dimensional lattice with on-site repulsion is presented. In one
dimension, the analytic calculation is in excellent agreement with the
numerical Monte Carlo results. In higher dimensions, the deviations from the
Monte Carlo calculations are larger, but the correct shape of the Mott
insulator lobes is still obtained. Explicit expressions for the energy of the
Mott and the ``defect'' phase are given in a strong-coupling expansion.Comment: RevTeX 3.
ElfStore: A Resilient Data Storage Service for Federated Edge and Fog Resources
Edge and fog computing have grown popular as IoT deployments become
wide-spread. While application composition and scheduling on such resources are
being explored, there exists a gap in a distributed data storage service on the
edge and fog layer, instead depending solely on the cloud for data persistence.
Such a service should reliably store and manage data on fog and edge devices,
even in the presence of failures, and offer transparent discovery and access to
data for use by edge computing applications. Here, we present Elfstore, a
first-of-its-kind edge-local federated store for streams of data blocks. It
uses reliable fog devices as a super-peer overlay to monitor the edge
resources, offers federated metadata indexing using Bloom filters, locates data
within 2-hops, and maintains approximate global statistics about the
reliability and storage capacity of edges. Edges host the actual data blocks,
and we use a unique differential replication scheme to select edges on which to
replicate blocks, to guarantee a minimum reliability and to balance storage
utilization. Our experiments on two IoT virtual deployments with 20 and 272
devices show that ElfStore has low overheads, is bound only by the network
bandwidth, has scalable performance, and offers tunable resilience.Comment: 24 pages, 14 figures, To appear in IEEE International Conference on
Web Services (ICWS), Milan, Italy, 201
Bose-Hubbard Models in Confining Potentials: An Inhomogeneous Mean-Field Theory
We present an extensive study of Mott insulator (MI) and superfluid (SF)
shells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic
traps. For this we develop an inhomogeneous mean-field theory. Our results for
the BH model with one type of spinless bosons agrees quantitatively with
quantum Monte Carlo (QMC) simulations. Our approach is numerically less
intensive than such simulations, so we are able to perform calculation on
experimentally realistic, large 3D systems, explore a wide range of parameter
values, and make direct contact with a variety of experimental measurements. We
also generalize our inhomogeneous mean-field theory to study BH models with
harmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two
species of bosons we obtain rich phase diagrams with a variety of SF and MI
phases and associated shells, when we include a quadratic confining potential.
For the spin-1 BH model we show, in a representative case, that the system can
display alternating shells of polar SF and MI phases; and we make interesting
predictions for experiments in such systems.Comment: 17 pages, 18 figure
Finite Temperature Phase Diagram in Rotating Bosonic Optical Lattice
Finite temperature phase boundary between superfluid phase and normal state
is analytically derived by studying the stability of normal state in rotating
bosonic optical lattice. We also prove that the oscillation behavior of
critical hopping matrix directly follows the upper boundary of Hofstadter
butterfly as the function of effective magnetic field.Comment: 10 pages, 2 figure
Rotating states for trapped bosons in an optical lattice
Rotational states for trapped bosons in an optical lattice are studied in the
framework of the Hubbard model. Critical frequencies are calculated and the
main parameter regimes are identified. Transitions are observed from edge
superfluids to vortex lattices with Mott insulating cores, and subsequently to
lattices of interstitial vortices. The former transition coincides with the
Mott transition. Changes in symmetry of the vortex lattices are observed as a
function of lattice depth. Predictions for experimental signatures are
presented.Comment: 6 pages, 6 figures, accepted for publication in EP
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