64,044 research outputs found
Quantum trajectories and open many-body quantum systems
The study of open quantum systems has become increasingly important in the
past years, as the ability to control quantum coherence on a single particle
level has been developed in a wide variety of physical systems. In quantum
optics, the study of open systems goes well beyond understanding the breakdown
of quantum coherence. There, the coupling to the environment is sufficiently
well understood that it can be manipulated to drive the system into desired
quantum states, or to project the system onto known states via feedback in
quantum measurements. Many mathematical frameworks have been developed to
describe such systems, which for atomic, molecular, and optical (AMO) systems
generally provide a very accurate description of the open quantum system on a
microscopic level. In recent years, AMO systems including cold atomic and
molecular gases and trapped ions have been applied heavily to the study of
many-body physics, and it has become important to extend previous understanding
of open system dynamics in single- and few-body systems to this many-body
context. A key formalism that has already proven very useful in this context is
the quantum trajectories technique. This was developed as a numerical tool for
studying dynamics in open quantum systems, and falls within a broader framework
of continuous measurement theory as a way to understand the dynamics of large
classes of open quantum systems. We review the progress that has been made in
studying open many-body systems in the AMO context, focussing on the
application of ideas from quantum optics, and on the implementation and
applications of quantum trajectories methods. Control over dissipative
processes promises many further tools to prepare interesting and important
states in strongly interacting systems, including the realisation of parameter
regimes in quantum simulators that are inaccessible via current techniques.Comment: 66 pages, 29 figures, review article submitted to Advances in Physics
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Steering in computational science: mesoscale modelling and simulation
This paper outlines the benefits of computational steering for high
performance computing applications. Lattice-Boltzmann mesoscale fluid
simulations of binary and ternary amphiphilic fluids in two and three
dimensions are used to illustrate the substantial improvements which
computational steering offers in terms of resource efficiency and time to
discover new physics. We discuss details of our current steering
implementations and describe their future outlook with the advent of
computational grids.Comment: 40 pages, 11 figures. Accepted for publication in Contemporary
Physic
Partitioning a macroscopic system into independent subsystems
We discuss the problem of partitioning a macroscopic system into a collection
of independent subsystems. The partitioning of a system into replica-like
subsystems is nowadays a subject of major interest in several field of
theoretical and applied physics, and the thermodynamic approach currently
favoured by practitioners is based on a phenomenological definition of an
interface energy associated with the partition, due to a lack of easily
computable expressions for a microscopic (i.e.~particle-based) interface
energy. In this article, we outline a general approach to derive sharp and
computable bounds for the interface free energy in terms of microscopic
statistical quantities. We discuss potential applications in nanothermodynamics
and outline possible future directions.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in JSTA
Geometric Cluster Algorithm for Interacting Fluids
We discuss a new Monte Carlo algorithm for the simulation of complex fluids.
This algorithm employs geometric operations to identify clusters of particles
that can be moved in a rejection-free way. It is demonstrated that this
geometric cluster algorithm (GCA) constitutes the continuum generalization of
the Swendsen-Wang and Wolff cluster algorithms for spin systems. Because of its
nonlocal nature, it is particularly well suited for the simulation of fluid
systems containing particles of widely varying sizes. The efficiency
improvement with respect to conventional simulation algorithms is a rapidly
growing function of the size asymmetry between the constituents of the system.
We study the cluster-size distribution for a Lennard-Jones fluid as a function
of density and temperature and provide a comparison between the generalized GCA
and the hard-core GCA for a size-asymmetric mixture with Yukawa-type couplings.Comment: To appear in "Computer Simulation Studies in Condensed-Matter Physics
XVII". Edited by D.P. Landau, S.P. Lewis and H.B. Schuettler. Springer,
Heidelberg, 200
Interaction effects in assembly of magnetic nanoparticles
A specific absorption rate of a dilute assembly of various random clusters of
iron oxide nanoparticles in alternating magnetic field has been calculated
using Landau- Lifshitz stochastic equation. This approach simultaneously takes
into account both the presence of thermal fluctuations of the nanoparticle
magnetic moments, and magneto-dipole interaction between the nanoparticles of
the clusters. It is shown that for usual 3D clusters the intensity of magneto-
dipole interaction is determined mainly by the cluster packing density eta =
Np*V/Vcl, where Np is the average number of the particles in the cluster, V is
the nanoparticle volume, and Vcl is the cluster volume. The area of the low
frequency hysteresis loop and the assembly specific absorption rate have been
found to be considerably reduced when the packing density of the clusters
increases in the range of 0.005 < eta < 0.4. The dependence of the specific
absorption rate on the mean nanoparticle diameter is retained with increase of
eta, but becomes less pronounced. For fractal clusters of nanoparticles, which
arise in biological media, in addition to considerable reduction of the
absorption rate, the absorption maximum is shifted to smaller particle
diameters. It is found also that the specific absorption rate of fractal
clusters increases appreciably with increase of the thickness of nonmagnetic
shells at the nanoparticle surfaces.Comment: The paper is accepted for Nanoscale Res. Let
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