18,824 research outputs found
Heralded high-efficiency quantum repeater with atomic ensembles assisted by faithful single-photon transmission
Quantum repeater is one of the important building blocks for long distance
quantum communication network. The previous quantum repeaters based on atomic
ensembles and linear optical elements can only be performed with a maximal
success probability of 1/2 during the entanglement creation and entanglement
swapping procedures. Meanwhile, the polarization noise during the entanglement
distribution process is harmful to the entangled channel created. Here we
introduce a general interface between a polarized photon and an atomic ensemble
trapped in a single-sided optical cavity, and with which we propose a
high-efficiency quantum repeater protocol in which the robust entanglement
distribution is accomplished by the stable spatial-temporal entanglement and it
can in principle create the deterministic entanglement between neighboring
atomic ensembles in a heralded way as a result of cavity quantum
electrodynamics. Meanwhile, the simplified parity check gate makes the
entanglement swapping be completed with unity efficiency, other than 1/2 with
linear optics. We detail the performance of our protocol with current
experimental parameters and show its robustness to the imperfections, i.e.,
detuning and coupling variation, involved in the reflection process. These good
features make it a useful building block in long distance quantum
communication.Comment: 11 pages, 10 figure
Error-rejecting quantum computing with solid-state spins assisted by low-Q optical microcavities
We present an efficient proposal for error-rejecting quantum computing with
quantum dots (QD) embedded in single-sided optical microcavities based on the
interface between the circularly polarized photon and QDs. An almost unity
fidelity of the quantum entangling gate (EG) can be implemented with a
detectable error that leads to a recycling EG procedure, which improves further
the efficiency of our proposal along with the robustness to the errors involved
in imperfect input-output processes. Meanwhile, we discuss the performance of
our proposal for the EG on two solid-state spins with currently achieved
experiment parameters, showing that it is feasible with current experimental
technology. It provides a promising building block for solid-state quantum
computing and quantum networks.Comment: 8 pages, 3 figure
Heralded quantum repeater for a quantum communication network based on quantum dots embedded in optical microcavities
We propose a heralded quantum repeater protocol based on the general
interface between the circularly polarized photon and the quantum dot embedded
in a double-sided optical microcavity. Our effective time-bin encoding on
photons results in the deterministic faithful entanglement distribution with
one optical fiber for the transmission of each photon in our protocol, not two
or more. Our efficient parity-check detector implemented with only one
input-output process of a single photon as a result of cavity quantum
electrodynamics makes the entanglement channel extension and entanglement
purification in quantum repeater far more efficient than others, and it has the
potential application in fault-tolerant quantum computation as well. Meanwhile,
the deviation from a collective-noise channel leads to some phase-flip errors
on the nonlocal electron spins shared by the parties and these errors can be
depressed by our simplified entanglement purification process. Finally, we
discuss the performance of our proposal, concluding that it is feasible with
current technology.Comment: 15 pages, 5 figure
Efficient Discriminative Nonorthogonal Binary Subspace with its Application to Visual Tracking
One of the crucial problems in visual tracking is how the object is
represented. Conventional appearance-based trackers are using increasingly more
complex features in order to be robust. However, complex representations
typically not only require more computation for feature extraction, but also
make the state inference complicated. We show that with a careful feature
selection scheme, extremely simple yet discriminative features can be used for
robust object tracking. The central component of the proposed method is a
succinct and discriminative representation of the object using discriminative
non-orthogonal binary subspace (DNBS) which is spanned by Haar-like features.
The DNBS representation inherits the merits of the original NBS in that it
efficiently describes the object. It also incorporates the discriminative
information to distinguish foreground from background. However, the problem of
finding the DNBS bases from an over-complete dictionary is NP-hard. We propose
a greedy algorithm called discriminative optimized orthogonal matching pursuit
(D-OOMP) to solve this problem. An iterative formulation named iterative D-OOMP
is further developed to drastically reduce the redundant computation between
iterations and a hierarchical selection strategy is integrated for reducing the
search space of features. The proposed DNBS representation is applied to object
tracking through SSD-based template matching. We validate the effectiveness of
our method through extensive experiments on challenging videos with comparisons
against several state-of-the-art trackers and demonstrate its capability to
track objects in clutter and moving background.Comment: 15 page
Quantum simulation of Kibble-Zurek mechanism with a semiconductor electron charge qubit
The Kibble-Zurek mechanism provides a description of the topological
structure occurring in the symmetry breaking phase transitions, which may
manifest as the cosmological strings in the early universe or vortex lines in
the superfulid. A particularly intriguing analogy between Kibble-Zurek
mechanism and a text book quantum phenomenon, Landau-Zener transition has been
discovered, but is difficult to observe up to now. In recent years, there has
been broad interest in quantum simulations using different well-controlled
physical setups, in which full tunability allows access to unexplored parameter
regimes. Here we demonstrate a proof-of-principle quantum simulation of
Kibble-Zurek mechanism using a single electron charge qubit in double quantum
dot, set to behave as Landau-Zener dynamics. We measure the qubit states as a
function of driven pulse velocity and successfully reproduce Kibble-Zurek like
dependence of topological defect density on the quench rate. The high-level
controllability of semiconductor two-level system make it a platform to test
the key elements of topological defect formation process and shed a new insight
on the aspect of non-equilibrium phase transitions.Comment: 14 pages, 4 figure
Mixed soliton solutions of the defocusing nonlocal nonlinear Schrodinger equation
By using the Darboux transformation, we obtain two new types of
exponential-and-rational mixed soliton solutions for the defocusing nonlocal
nonlinear Schrodinger equation. We reveal that the first type of solution can
display a large variety of interactions among two exponential solitons and two
rational solitons, in which the standard elastic interaction properties are
preserved and each soliton could be either the dark or antidark type. By
developing the asymptotic analysis technique, we also find that the second type
of solution can exhibit the elastic interactions among four mixed asymptotic
solitons. But in sharp contrast to the common solitons, the asymptotic mixed
solitons have the t-dependent velocities and their phase shifts before and
after interaction also grow with |t| in the logarithmical manner. In addition,
we discuss the degenerate cases for such two types of mixed soliton solutions
when the four-soliton interaction reduces to a three-soliton or two-soliton
interaction.Comment: 28 pages, 7 figure
Self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom
Usually, the hyperparallel quantum computation can speed up quantum
computing, reduce the quantum resource consumed largely, resist to noise, and
simplify the storage of quantum information. Here, we present the first scheme
for the self-error-corrected hyperparallel photonic quantum computation working
with both the polarization and the spatial-mode degrees of freedom of photon
systems simultaneously. It can prevent bit-flip errors from happening with an
imperfect nonlinear interaction in the nearly realistic condition. We give the
way to design the universal hyperparallel photonic quantum controlled-NOT
(CNOT) gate on a two-photon system, resorting to the nonlinear interaction
between the circularly polarized photon and the electron spin in the quantum
dot in a double-sided microcavity system, by taking the imperfect interaction
in the nearly realistic condition into account. Its self-error-corrected
pattern prevents the bit-flip errors from happening in the hyperparallel
quantum CNOT gate, guarantees the robust fidelity, and relaxes the requirement
for its experiment. Meanwhile, this scheme works in a failure-heralded way.
Also, we generalize this approach to achieve the self-error-corrected
hyperparallel quantum CNOT gate working on a multiple-photon system. These
good features make this scheme more useful in the photonic quantum computation
and quantum communication in the future.Comment: One column, 11 pages, 3 figures. Compared with V2, we give a major
revision on this paper in the present versio
QCD inspired relativistic bound state model and meson structures
A QCD inspired relativistic effective Hamiltonian model for the bound states
of mesons has been constructed, which integrates the advantages of several QCD
effective Hamiltonian models. Based on light-front QCD effective Hamiltonian
model, the squared invariant mass operator of meson is used as the effective
Hamiltonian. The model has been improved significantly in four major aspects:
i)it is proved that in center of mass frame and in internal coordinate Hilbert
subspace, the total angular momentum of meson is conserved and the mass
eigen equation can be expressed in total angular momentum representation and in
terms of a set of coupled radial eigen equations for each . ii)Based on
lattice QCD results, a relativistic confining potential is introduced into the
effective interaction and the excited states of mesons can be well described.
iii)an SU(3) flavor mixing interaction is introduced phenomenologically to
describe the flavor mixing mesons and the mass eigen equations contain the
coupling among different flavor components. iv)the mass eigen equations are of
relativistic covariance and the coupled radial mass eigen equations take full
account of coupling and tensor interactions. The model has been applied
to describe the whole meson spectra of about 265 mesons with available data.
The agreement of the calculated masses, squared radii, and decay constants with
data is quite well. For the mesons whose mass data have large experimental
uncertainty, the model produces certain mass values for test. For some mesons
whose total angular momenta and parity are not assigned experimentally, the
model gives a prediction of the spectroscopic configuration. The
connection between our model and the recent low energy QCD issues-the infrared
conformal scaling invariance and holographic QCD hadron models is discussed.Comment: 16 page
Unitarity and Entropy Change in Exclusive Quark Combination Models
Entropy change in exclusive quark combination models is not an isolated
problem. Contrary to adding and tuning some parameters to the relevant model(s)
to fix the entropy, we show that it relates to the most general principles.
Unitarity of the combination model is demonstrated to play the central r\^{o}le
that guarantees the non-decrease of the entropy in the exclusive combination
process.Comment: 4 pages in revtex, 1 figure, a ref. adde
Adaptive Affinity Propagation Clustering
Affinity propagation clustering (AP) has two limitations: it is hard to know
what value of parameter 'preference' can yield an optimal clustering solution,
and oscillations cannot be eliminated automatically if occur. The adaptive AP
method is proposed to overcome these limitations, including adaptive scanning
of preferences to search space of the number of clusters for finding the
optimal clustering solution, adaptive adjustment of damping factors to
eliminate oscillations, and adaptive escaping from oscillations when the
damping adjustment technique fails. Experimental results on simulated and real
data sets show that the adaptive AP is effective and can outperform AP in
quality of clustering results.Comment: an English version of original pape
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