11,200 research outputs found
Weaving independently generated photons into an arbitrary graph state
The controlled Z (CZ) operations acting separately on pairs of qubits are
commonly adopted in the schemes of generating graph states, the multi-partite
entangled states for the one-way quantum computing. For this purpose, we
propose a setup of cascade CZ operation on a whole group of qubits in sequence.
The operation of the setup starts with entangling an ancilla photon to the
first photon as qubit, and this ancilla automatically moves from one
entanglement link to another in assisting the formation of a string in graph
states. The generation of some special types of graph states, such as the
three-dimensional ones, can be greatly simplified in this approach. The setup
presented uses weak nonlinearities, but an implementation using probabilistic
linear optics is also possible.Comment: 6 pages, 7 figures. Accepted by Phys. Rev.
Highly Efficient Processing Multi-photon States
How to implement multi-qubit gates is an important problem in quantum
information processing. Based on cross phase modulation, we present an approach
to realizing a family of multi-qubit gates that deterministically operate on
single photons as the qubits. A general -qubit unitary operation is a
typical example of these gates. The approach greatly relax the requirement on
the resources, such as the ancilla photons and coherent beams, as well as the
number of operations on the qubits. The improvement in this framework may
facilitate large scale quantum information processing.Comment: to be published in Scientific Reports. 14 pages, 5 figures (plus 5
pages and 2 figures in supplementary materials
Impact on from CLEO-c Using CP-tagged D\toK_{S,L}\pi\pi Decays
Precision determination of the CKM angle depends upon
constraints on charm mixing amplitudes, measurements of doubly-Cabibbo
suppressed amplitudes and relative phases, and studies of charm Dalitz plots
tagged by flavor or CP eigenstates. In this note we describe the technique used
at CLEO-c to constrain the model uncertainty, and its impact on
measurements at B-factories presented at the Charm 2007
Workshop.Comment: 5 pages, 5 figures, submitted to Charm 2007 Workshop Conference
proceeding
Multiple-relaxation-time lattice Boltzmann model for simulating double-diffusive convection in fluid-saturated porous media
Double-diffusive convection in porous media is a common phenomenon in nature,
and has received considerable attention in a wide variety of engineering
applications. In this paper, a multiple-relaxation-time (MRT) lattice Boltzmann
(LB) model is developed for simulating double-diffusive convection in porous
media at the representative elementary volume scale. The MRT-LB model is
constructed in the framework of the triple-distribution-function approach: the
velocity field, the temperature and concentration fields are solved separately
by three different MRT-LB equations. The present model has two distinctive
features. First, the equilibrium moments of the temperature and concentration
distributions have been modified, which makes the effective thermal diffusivity
and heat capacity ratio as well as the effective mass diffusivity and porosity
decoupled . This feature is very useful in practical applications. Second,
source terms have been added into the MRT-LB equations of the temperature and
concentration fields so as to recover the macroscopic temperature and
concentration equations. Numerical tests demonstrate that the present model can
serve as an accurate and efficient numerical method for simulating
double-diffusive convection in porous media
Cascaded Channel Estimation for Large Intelligent Metasurface Assisted Massive MIMO
In this letter, we consider the problem of channel estimation for large
intelligent metasurface (LIM) assisted massive multiple-input multiple-output
(MIMO) systems. The main challenge of this problem is that the LIM integrated
with a large number of low-cost metamaterial antennas can only passively
reflect the incident signal by a certain phase shift, and does not have any
signal processing capability. To deal with this, we introduce a general
framework for the estimation of the transmitter-LIM and LIM-receiver cascaded
channel, and propose a two-stage algorithm that includes a sparse matrix
factorization stage and a matrix completion stage. Simulation results
illustrate that the proposed method can achieve accurate channel estimation for
LIM-assisted massive MIMO systems.Comment: 3 figures, 5 page
Approach of background metric expansion to a new metric ansatz for gauged and ungauged Kaluza-Klein supergravity black holes
In a previous paper [S.Q. Wu, Phys. Rev. D 83, 121502(R) (2011)], a new kind
of metric ansatz was found to fairly describe all already known black hole
solutions in the ungauged Kaluza-Klein (KK) supergravity theories. That metric
ansatz somewhat resembles to the famous Kerr-Schild (KS) form, but it is
different from the KS one in two distinct aspects. That is, apart from a global
conformal factor, the metric ansatz can be written as a vacuum background
spacetime plus a "perturbation" modification term, the latter of which is
associated with a timelike geodesic vector field rather than a null geodesic
congruence in the usual KS ansatz. In this paper, we shall study this novel
metric ansatz in detail, aiming at achieving some inspiration as to the
construction of rotating charged AdS black holes with multiple charges in other
gauged supergravity theories. In order to investigate the metric properties of
the general KK-AdS solutions, in this paper we devise a new effective method,
dubbed the background metric expansion method, which can be thought of as a
generalization of the perturbation expansion method, to deal with the
Lagrangian and all equations of motion. In addition to two previously known
conditions, namely the timelike and geodesic properties of the vector, we get
the three additional constraints via contracting the Maxwell and Einstein
equations once or twice with this timelike geodesic vector. In particular, we
find that these are a simple set of sufficient conditions to determine the
vector and the dilaton scalar around the background metric, which is helpful in
obtaining new exact solutions. With these five simplified equations in hand, we
rederive the general rotating charged KK-(A)dS black hole solutions with
spherical horizon topology and obtain new solutions with planar topology in all
dimensions.Comment: 9 pages, Revtex4.cls, version mathched with the published pape
Double multiple-relaxation-time lattice Boltzmann model for solid-liquid phase change with natural convection in porous media
In this paper, a double multiple-relaxation-time lattice Boltzmann model is
developed for simulating transient solid-liquid phase change problems in porous
media at the representative elementary volume scale. The model uses two
different multiple-relaxation-time lattice Boltzmann equations, one for the
flow field and the other for the temperature field with nonlinear latent heat
source term. The model is based on the generalized non-Darcy formulation, and
the solid-liquid phase change interface is traced through the liquid fraction
which is determined by the enthalpy method. The model is validated by numerical
simulations of conduction melting in a semi-infinite space, solidification in a
semi-infinite corner, and convection melting in a square cavity filled with
porous media. The numerical results demonstrate the efficiency and accuracy of
the present model for simulating transient solid-liquid phase change problems
in porous media.Comment: 29 pages, 11 figure
A multiple-relaxation-time lattice Boltzmann model for convection heat transfer in porous media
In this paper, a two-dimensional (2D) multiple-relaxation-time (MRT) lattice
Boltzmann (LB) model is developed for simulating convection heat transfer in
porous media at the representative elementary volume scale. In the model, a
MRT-LB equation is used to simulate the flow field, while another MRT-LB
equation is employed to simulate the temperature field. The effect of the
porous media is considered by introducing the porosity into the equilibrium
moments, and adding a forcing term to the MRT-LB equation of the flow field in
the moment space. The present MRT-LB model is validated by numerical
simulations of several 2D convection problems in porous media. The numerical
results are in good agreement with the well-documented data reported in the
literature.Comment: 37 pages, 7 figure
A Fast, Semi-Automatic Brain Structure Segmentation Algorithm for Magnetic Resonance Imaging
Medical image segmentation has become an essential technique in clinical and
research-oriented applications. Because manual segmentation methods are
tedious, and fully automatic segmentation lacks the flexibility of human
intervention or correction, semi-automatic methods have become the preferred
type of medical image segmentation. We present a hybrid, semi-automatic
segmentation method in 3D that integrates both region-based and boundary-based
procedures. Our method differs from previous hybrid methods in that we perform
region-based and boundary-based approaches separately, which allows for more
efficient segmentation. A region-based technique is used to generate an initial
seed contour that roughly represents the boundary of a target brain structure,
alleviating the local minima problem in the subsequent model deformation phase.
The contour is deformed under a unique force equation independent of image
edges. Experiments on MRI data show that this method can achieve high accuracy
and efficiency primarily due to the unique seed initialization technique
Breaking optomechanical cooling limit by two drive fields on a membrane-in-middle system
We present a theoretical scheme for ground state cooling of a mechanical
resonator in a membrane-in-middle optomechanical system (OMS) driven by two
red-detuned drive fields. The details of dynamical evolution of OMS are
provided, and the effect of system conditions on cooling results are
systematically studied. Most importantly, the setups with two drives are found
to be capable of achieving better cooling results than the theoretical cooling
limit with single cavity. Even an improvement by one order of thermal phonon
number is possible with proper combination of the cavity damping rate and drive
intensity.Comment: 10 pages, 6 figures, accepted by Physical Review
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