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 Fr$\rm\ddot o$hlich 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 J/ψJ/\psi production in cold nuclear matter

$J/\psi$ 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 $c\overline{c}$. The leading-order computations for $J/\psi$ production cross-section ratios $R_{W/Be}(x_{F})$ are presented and compared with the selected E866 experimental data with the $c\overline{c}$ 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 $J/\psi$ suppression in the experimental data. It is found that the $J/\psi$ suppression on $R_{W/Be}(x_{F})$ from the initial state nuclear effects is more important than that induced by the energy loss of color octet $c\overline{c}$ in the large $x_F$ region. Whether the $c\overline{c}$ pair energy loss is linear or quadratic with the path length is not determined. The obtained $c\overline{c}$ pair energy loss per unit path length $\alpha=2.78\pm0.81$ 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