52,004 research outputs found
Quantum Communication Through a Spin-Ring with Twisted Boundary Conditions
We investigate quantum communication between the sites of a spin-ring with
twisted boundary conditions. Such boundary conditions can be achieved by a flux
through the ring. We find that a non-zero twist can improve communication
through finite odd numbered rings and enable high fidelity multi-party quantum
communication through spin rings (working near perfectly for rings of 5 and 7
spins). We show that in certain cases, the twist results in the complete
blockage of quantum information flow to a certain site of the ring. This effect
can be exploited to interface and entangle a flux qubit and a spin qubit
without embedding the latter in a magnetic field.Comment: four pages two figure
Photo-emission rate of sQGP at finite density
We calculate the thermal spectral function of SYM plasma with finite density
using holographic technique. We take the RN-AdS black hole as the dual gravity
theory. In the presence of charge, vector modes of gravitational and
electromagnetic perturbation are coupled with each other. By introducing master
variables for these modes, we solve the coupled system and calculate spectral
function. We also calculated photoemission rate of SYM plasma from spectral
function for light like momentum, AC conductivity and their density dependence.
The suppression of the conductivity in high density is noticed, which might be
yet another mechanism for the Jet quenching phenomena in RHIC experiment.Comment: 27 pages, 10 figure
A temperature and magnetic field dependence Mössbauer study of ɛ-Fe2O3
ɛ-Fe2O3 was synthesized as nanoparticles by a pre-vacuum heat treatment of yttrium iron garnet (Y3Fe5O12) in a silica matrix at 300-C followed by sintering in air at 1,000-C for up to 10 h. It displays complex magnetic properties that are characterized by two transitions, one at 480 K from a paramagnet (P) to canted antiferromagnet (CAF1) and the second at ca. 120 K from the canted antiferromagnet (CAF1) to another canted antiferromagnet (CAF2). CAF2 has a smaller resultant magnetic moment (i.e. smaller canting angle) than CAF1. Analysis of the zero-field Mossbauer spectra at different temperatures shows an associated discontinuity of the hyperfine field around 120 K. In an applied field, the different magnetic sublattices were identified and the directions of their moments were assigned. The moments of the two sublattices are antiparallel and collinear at 160 K but are at right angle to each other at 4.2 K
New physics effects on top quark spin correlation and polarization at the LHC: a comparative study in different models
Extensions of the Standard Model often predict new chiral interactions for
top quark, which will contribute to top quark spin correlation and polarization
in production at the LHC. In this work, under the constraints from
the current Tevatron measurements, a comparative study of the spin correlation
and polarization is performed in three new physics models: the minimal
supersymmetric model without R-parity (RPV-MSSM), the third-generation enhanced
left-right model and the axigluon model. We find that the polarization
asymmetry may be enhanced to the accessible level in all these models while the
correction to the spin correlation may be detectable in the axigluon model and
the RPV-MSSM with couplings.Comment: Version in PRD (figs updated and discussions added
Ant colony optimization with immigrants schemes in dynamic environments
This is the post-print version of this article. The official published version can be accessed from the link below - Copyright @ 2010 Springer-VerlagIn recent years, there has been a growing interest in addressing dynamic optimization problems (DOPs) using evolutionary algorithms (EAs). Several approaches have been developed for EAs to increase the diversity of the population and enhance the performance of the algorithm for DOPs. Among these approaches, immigrants schemes have been found beneficial for EAs for DOPs. In this paper, random, elitismbased, and hybrid immigrants schemes are applied to ant colony optimization (ACO) for the dynamic travelling salesman problem (DTSP). The experimental results show that random immigrants are beneficial for ACO in fast changing environments, whereas elitism-based immigrants are beneficial for ACO in slowly changing environments. The ACO algorithm with hybrid immigrants scheme combines the merits of the random and elitism-based immigrants schemes. Moreover, the results show that the proposed algorithms outperform compared approaches in almost all dynamic test cases and that immigrant schemes efficiently improve the performance of ACO algorithms in DTSP.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1
Memory-based immigrants for ant colony optimization in changing environments
Copyright @ 2011 SpringerAnt colony optimization (ACO) algorithms have proved that they can adapt to dynamic optimization problems (DOPs) when they are enhanced to maintain diversity. DOPs are important due to their similarities to many real-world applications. Several approaches have been integrated with ACO to improve their performance in DOPs, where memory-based approaches and immigrants schemes have shown good results on different variations of the dynamic travelling salesman problem (DTSP). In this paper, we consider a novel variation of DTSP where traffic jams occur in a cyclic pattern. This means that old environments will re-appear in the future. A hybrid method that combines memory and immigrants schemes is proposed into ACO to address this kind of DTSPs. The memory-based approach is useful to directly move the population to promising areas in the new environment by using solutions stored in the memory. The immigrants scheme is useful to maintain the diversity within the population. The experimental results based on different test cases of the DTSP show that the memory based immigrants scheme enhances the performance of ACO in cyclic dynamic environments.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/2
Temperature - pressure phase diagram of the superconducting iron pnictide LiFeP
Electrical-resistivity and magnetic-susceptibility measurements under
hydrostatic pressure up to p = 2.75 GPa have been performed on superconducting
LiFeP. A broad superconducting (SC) region exists in the temperature - pressure
(T-p) phase diagram. No indications for a spin-density-wave transition have
been found, but an enhanced resistivity coefficient at low pressures hints at
the presence of magnetic fluctuations. Our results show that the
superconducting state in LiFeP is more robust than in the isostructural and
isoelectronic LiFeAs. We suggest that this finding is related to the nearly
regular [FeP_4] tetrahedron in LiFeP.Comment: 4 pages, 4 figure
Recent Experiments with Bose-Condensed Gases at JILA
We consider a binary mixture of two overlapping Bose-Einstein condensates in
two different hyperfine states of \Rb87 with nearly identical magnetic moments.
Such a system has been simply realized through application of radiofrequency
and microwave radiation which drives a two-photon transition between the two
states. The nearly identical magnetic moments afford a high degree of spatial
overlap, permitting a variety of new experiments. We discuss some of the
conditions under which the magnetic moments are identical, with particular
emphasis placed on the requirements for a time-averaged orbiting potential
(TOP) magnetic trap.Comment: 9 pages, 5 figures; corrected post-publication editio
Production Efficiency of Ultracold Feshbach Molecules in Bosonic and Fermionic Systems
We investigate the production efficiency of ultracold molecules in bosonic
Rb and fermionic K when the magnetic field is swept across a
Feshbach resonance. For adiabatic sweeps of the magnetic field, the conversion
efficiency of each species is solely determined by the phase space density of
the atomic cloud, in contrast to a number of theoretical predictions. Our novel
model for the adiabatic pairing process, developed from general physical
principles, accurately predicts the conversion efficiency for {\it both}
ultracold gases of bosons and of fermions. In the non-adiabatic regime our
measurements of the Rb molecule conversion efficiency follow a Landau
Zener model, with a conversion efficiency that is characterized by the density
divided by the time derivative of the magnetic field.Comment: 5 pages, 3 figure
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