3,514 research outputs found
One-party Quantum Error Correcting Codes for Unbalanced Errors: Principles and Application to Quantum Dense Coding and Quantum Secure Direct Communications
In this article, we present the unbalanced quantum error correcting
codes(one-party-QECC), a novel idea for correcting unbalanced quantum errors.
In some quantum communication tasks using entangled pairs, the error
distributions between two parts of the pairs are unbalanced, and. one party
holds the whole entangled pairs at the final stage, and he or she is able to
perform joint measurements on the pairs. In this situation the proposed
one-party-QECC can improve error correction by allowing a higher tolerated
error rate. We have established the general correspondence between linear
classical codes and the one-party-QECC, and we have given the general
definition for this type quantum error correcting codes.It has been shown that
the one-party-QECC can correct errors as long as the error threshold is not
larger than 0.5. The one-party-QECC works even for fidelity less than 0.5 as
long as it is larger than 0.25. We give several concrete examples of the
one-party-QECC. We provide the applications of one-party-QECC in quantum dense
coding so that it can function in noisy channels. As a result, a large number
of quantum secure direct communication protocols based on dense coding is also
able to be protected by this new type of one-party-QECC.Comment: 15 pages and 2 figures and 3 table
Exact magnetic field control of nitrogen-vacancy center spin for realizing fast quantum logic gates
The negatively charged nitrogen-vacancy (NV) center spin in diamond can be
used to realize quantum computation and to sense magnetic fields. Its spin
triplet consists of three levels labeled with its spin z-components of +1, 0,
and -1. Without external field, the +1 and -1 states are degenerate and higher
than the 0 state due to the zero-field splitting. By taking the symmetrical and
anti-symmetrical superpositions of the +1 and -1 states as our qubit basis, we
obtain exact evolution operator of the NV center spin under time-dependent
magnetic field by mapping the three-level system on time-dependent quantum
two-level systems with exact analytical solutions. With our exact evolution
operator of the NV center spin including three levels, we show that arbitrary
qubits can be prepared from the starting 0 state and arbitrary rapid quantum
logic gates of these qubits can be realized with magnetic fields. In addition,
it is made clear that the typical quantum logic gates can be accomplished
within a few nanoseconds and the fidelity can be very high because only
magnetic field strength needs to be controlled in this approach. These results
should be useful to realizing quantum computing with the NV center spin systems
in diamond and exploring other effects and applications.Comment: 7 pages including 3 figure
Fast magnetic field manipulations and nonadiabatic geometric phases of nitrogen-vacancy center spin in diamond
Fast quantum spin manipulation is needed to design spin-based quantum logic
gates and other quantum applications. Here, we construct exact evolution
operator of the nitrogen-vacancy-center (NV) spin in diamond under external
magnetic fields and investigate the nonadiabatic geometric phases, both cyclic
and non-cyclic, in these fast-manipulated NV spin systems. It is believed that
the nonadiabatic geometric phases can be measured in future experiments and
these fast quantum manipulations can be useful in designing spin-based quantum
applications.Comment: 5 pages, 4 figure
Generating Squeezed States of Nanomechanical Resonator
We propose a scheme for generating squeezed states in solid state circuits
consisting of a nanomechanical resonator (NMR), a superconducting Cooper-pair
box (CPB) and a superconducting transmission line resonator (STLR). The
nonlinear interaction between the NMR and the STLR can be implemented by
setting the external biased flux of the CPB at certain values. The interaction
Hamiltonian between the NMR and the STLR is derived by performing Frhlich transformation on the total Hamiltonian of the combined system. Just by
adiabatically keeping the CPB at the ground state, we get the standard
parametric down-conversion Hamiltonian. The CPB plays the role of ``nonlinear
media", and the squeezed states of the NMR can be easily generated in a manner
similar to the three-wave mixing in quantum optics. This is the three-wave
mixing in a solid-state circuit.Comment: 4 pages 1 figure. One figure added, squeezing efficiency added. Noise
considere
Meaningful Objects Segmentation from SAR Images via A Multi-Scale Non-Local Active Contour Model
The segmentation of synthetic aperture radar (SAR) images is a longstanding
yet challenging task, not only because of the presence of speckle, but also due
to the variations of surface backscattering properties in the images.
Tremendous investigations have been made to eliminate the speckle effects for
the segmentation of SAR images, while few work devotes to dealing with the
variations of backscattering coefficients in the images. In order to overcome
both the two difficulties, this paper presents a novel SAR image segmentation
method by exploiting a multi-scale active contour model based on the non-local
processing principle. More precisely, we first formulize the SAR segmentation
problem with an active contour model by integrating the non-local interactions
between pairs of patches inside and outside the segmented regions. Secondly, a
multi-scale strategy is proposed to speed up the non-local active contour
segmentation procedure and to avoid falling into local minimum for achieving
more accurate segmentation results. Experimental results on simulated and real
SAR images demonstrate the efficiency and feasibility of the proposed method:
it can not only achieve precise segmentations for images with heavy speckles
and non-local intensity variations, but also can be used for SAR images from
different types of sensors
Proof of Security of a High-Capacity Quantum Key Distribution Protocol
We prove the security of a high-capacity quantum key distribution protocol
over noisy channels. By using entanglement purification protocol, we construct
a modified version of the protocol in which we separate it into two consecutive
stages. We prove their securities respectively and hence the security of the
whole protocol.Comment: 4 page
Secure Reusable Base-String in Quantum Key Distribution
Protecting secure random key from eavesdropping in quantum key distribution
protocols has been well developed. In this letter, we further study how to
detect and eliminate eavesdropping on the random base string in such protocols.
The correlation between the base string and the key enables Alice and Bob to
use specific privacy amplification to distill and reuse the previously shared
base string with unconditional security and high efficiency. The analysis of
the unconditional secure reusable base string brings about new concept and
protocol design technique.Comment: 4 pages and 3 figure
Simulation of four-body interaction in a nuclear magnetic resonance quantum information processor
Four-body interaction plays an important role in many-body systems, and it
can exhibit interesting phase transition behaviors. Historically it was the
need to efficiently simulate quantum systems that lead the idea of a quantum
computer. In this Letter, we report the experimental demonstration of a
four-body interaction in a four- qubit nuclear magnetic resonance quantum
information processor. The strongly modulating pulse is used to implement spin
selective excitation. The results show a good agreement between theory and
experiment.Comment: 4 pages 5 figure
Energy loss of charm quarks from production in cold nuclear matter
suppression in p-A collisions is studied by considering the nuclear
effects on parton distribution, energy loss of beam proton and the finial state
energy loss of color octet . The leading-order computations for
production cross-section ratios are presented and
compared with the selected E866 experimental data with the
remaining colored on its entire path in the medium. It is shown that the
combination of the different nuclear effects accounts quite well for the
observed suppression in the experimental data. It is found that the
suppression on from the initial state nuclear
effects is more important than that induced by the energy loss of color octet
in the large region. Whether the pair
energy loss is linear or quadratic with the path length is not determined. The
obtained pair energy loss per unit path length
GeV/fm, which indicates that the heavy quark in cold
nuclear matter can lose more energy compared to the outgoing light quark
Large Margin Multi-modal Multi-task Feature Extraction for Image Classification
The features used in many image analysis-based applications are frequently of
very high dimension. Feature extraction offers several advantages in
high-dimensional cases, and many recent studies have used multi-task feature
extraction approaches, which often outperform single-task feature extraction
approaches. However, most of these methods are limited in that they only
consider data represented by a single type of feature, even though features
usually represent images from multiple modalities. We therefore propose a novel
large margin multi-modal multi-task feature extraction (LM3FE) framework for
handling multi-modal features for image classification. In particular, LM3FE
simultaneously learns the feature extraction matrix for each modality and the
modality combination coefficients. In this way, LM3FE not only handles
correlated and noisy features, but also utilizes the complementarity of
different modalities to further help reduce feature redundancy in each
modality. The large margin principle employed also helps to extract strongly
predictive features so that they are more suitable for prediction (e.g.,
classification). An alternating algorithm is developed for problem optimization
and each sub-problem can be efficiently solved. Experiments on two challenging
real-world image datasets demonstrate the effectiveness and superiority of the
proposed method
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