2,332 research outputs found
Cycle-time properties of the timed token medium access control protocol
We investigate the timing properties of the timed token protocol that are necessary to guarantee synchronous message deadlines. A tighter upper bound on the elapse time between the token's lth arrival at any node i and its (l + v)th arrival at any node k is found. A formal proof to this generalized bound is presented
Simulation studies for dielectric wakefield programme at CLARA facility
Short, high charge electron bunches can drive high magnitude electric fields
in dielectric lined structures. The interaction of the electron bunch with this
field has several applications including high gradient dielectric wakefield
acceleration (DWA) and passive beam manipulation. The simulations presented
provide a prelude to the commencement of an experimental DWA programme at the
CLARA accelerator at Daresbury Laboratory. The key goals of this program are:
tunable generation of THz radiation, understanding of the impact of transverse
wakes, and design of a dechirper for the CLARA FEL. Computations of
longitudinal and transverse phase space evolution were made with Impact-T and
VSim to support both of these goals.Comment: 10 Pages, 4 Figures, Proceedings of EAAC2017 Conferenc
Coherent transport in a two-electron quantum dot molecule
We investigate the dynamics of two interacting electrons confined to a pair
of coupled quantum dots driven by an external AC field. By numerically
integrating the two-electron Schroedinger equation in time, we find that for
certain values of the strength and frequency of the AC field we can cause the
electrons to be localised within the same dot, in spite of the Coulomb
repulsion between them. Reducing the system to an effective two-site model of
Hubbard type and applying Floquet theory leads to a detailed understanding of
this effect. This demonstrates the possibility of using appropriate AC fields
to manipulate entangled states in mesoscopic devices on extremely short
timescales, which is an essential component of practical schemes for quantum
information processing.Comment: 4 pages, 3 figures; the section dealing with the perturbative
treatment of the Floquet states has been substantially expanded to make it
easier to follo
Stability of strangelet at finite temperature
Using the quark mass density- and temperature dependent model, we have
studied the thermodynamical properties and the stability of strangelet at
finite temperature. The temperature, charge and strangeness dependences on the
stability of strangelet are investigated. We find that the stable strangelets
are only occured in the high strangeness and high negative charge region.Comment: 12 pages, 14 figure
Intrinsic determination of pH using a barycentre algorithm to characterise fluorescence from an optical fibre sensor
An algorithm to determine the barycentre of the signal received from a fluorescence-based fibre optic sensor probe has been implemented for the intrinsic characterisation of the fluorescence spectra of a pH sensor using coumarin dyes
A Quantum Hall Fluid of Vortices
In this note we demonstrate that vortices in a non-relativistic Chern-Simons
theory form a quantum Hall fluid. We show that the vortex dynamics is
controlled by the matrix mechanics previously proposed by Polychronakos as a
description of the quantum Hall droplet. As the number of vortices becomes
large, they fill the plane and a hydrodynamic treatment becomes possible,
resulting in the non-commutative theory of Susskind. Key to the story is the
recent D-brane realisation of vortices and their moduli spaces.Comment: 10 pages. v2(3): (More) References adde
A Detailed Monte-Carlo Simulation for the Belle TOF System
We have developed a detailed Monte Carlo simulation program for the Belle TOF
system. Based on GEANT simulation, it takes account of all physics processes in
the TOF scintillation counters and readout electronics. The simulation
reproduces very well the performance of the Belle TOF system, including the
dE/dx response, the time walk effect, the time resolution, and the hit
efficiency due to beam background. In this report, we will describe the Belle
TOF simulation program in detail.Comment: To be submitted to NI
Exact Master Equation and Non-Markovian Decoherence for Quantum Dot Quantum Computing
In this article, we report the recent progress on decoherence dynamics of
electrons in quantum dot quantum computing systems using the exact master
equation we derived recently based on the Feynman-Vernon influence functional
approach. The exact master equation is valid for general nanostructure systems
coupled to multi-reservoirs with arbitrary spectral densities, temperatures and
biases. We take the double quantum dot charge qubit system as a specific
example, and discuss in details the decoherence dynamics of the charge qubit
under coherence controls. The decoherence dynamics risen from the entanglement
between the system and the environment is mainly non-Markovian. We further
discuss the decoherence of the double-dot charge qubit induced by quantum point
contact (QPC) measurement where the master equation is re-derived using the
Keldysh non-equilibrium Green function technique due to the non-linear coupling
between the charge qubit and the QPC. The non-Markovian decoherence dynamics in
the measurement processes is extensively discussed as well.Comment: 15 pages, Invited article for the special issue "Quantum Decoherence
and Entanglement" in Quantum Inf. Proces
Quantum Entanglement of Excitons in Coupled Quantum Dots
Optically-controlled exciton dynamics in coupled quantum dots is studied. We
show that the maximally entangled Bell states and Greenberger-Horne-Zeilinger
(GHZ) states can be robustly generated by manipulating the system parameters to
be at the avoided crossings in the eigenenergy spectrum. The analysis of
population transfer is systematically carried out using a dressed-state
picture. In addition to the quantum dot configuration that have been discussed
by Quiroga and Johnson [Phys. Rev. Lett. \QTR{bf}{83}, 2270 (1999)], we show
that the GHZ states also may be produced in a ray of three quantum dots with a
shorter generation time.Comment: 16 pages, 7 figures, to appear in Phys. Rev.
Superconductors are topologically ordered
We revisit a venerable question: what is the nature of the ordering in a
superconductor? We find that the answer is properly that the superconducting
state exhibits topological order in the sense of Wen, i.e. that while it lacks
a local order parameter, it is sensitive to the global topology of the
underlying manifold and exhibits an associated fractionalization of quantum
numbers. We show that this perspective unifies a number of previous
observations on superconductors and their low lying excitations and that this
complex can be elegantly summarized in a purely topological action of the
``'' type and its elementary quantization. On manifolds with boundaries,
the action correctly predicts non-chiral edge states, gapped in general,
but crucial for fractionalization and establishing the ground state degeneracy.
In all of this the role of the physical electromagnetic fields is central. We
also observe that the action describes the topological order in several
other physically distinct systems thus providing an example of topological
universality
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