The negativity of Wigner function as a measure of quantum correlations

In this paper, we study comparatively the behaviors of Wigner function and quantum correlations for two quasi-Werner states formed with two general bipartite superposed coherent states. We show that the Wigner function can be used to detect and quantify the quantum correlations. However, we show that it is in fact not sensitive to all kinds of quantum correlations but only to entanglement. Then, we analyze the measure of non-classicality of quantum states based on the volume occupied by the negative part of the Wigner function.     

Revealing advantage in a quantum network

The assumption of source independence was used to reveal nonlocal (apart from standard Bell-CHSH scenario) nature of correlations generated in entanglement swapping experiments. In this work, we have discussed the various utilities of this assumption to reveal nonlocality (via generation of nonbilocal correlations) and thereby exploiting quantumness under lesser requirements compared to some standard means of doing the same. We have also provided with a set of sufficient criteria, imposed on the states (produced by the sources) under which source independence can reveal nonbilocal nature of correlations in a quantum network.     

Residual entanglement with negativity for pure four-qubit quantum states

In this work we study the entanglement of pure four-qubit quantum states. The analysis is realized, firstly, through the comparison between two different entanglement measures: the Groverian entanglement measure and the residual entanglement calculated with negativities. After, we use the last to measure the entanglement of several four-qubit states and the variation of the entanglement when the four-qubit state is processed by a two-qubit gate.     

Superactivation of quantum channels is limited by the quantum relative entropy function

In this work we prove that the possibility of superactivation of quantum channel capacities is determined by the mathematical properties of the quantum relative entropy function. Before our work this fundamental and purely mathematical connection between the quantum relative entropy function and the superactivation effect was completely unrevealed. We demonstrate the results for the quantum capacity; however the proposed theorems and connections hold for all other channel capacities of quantum channels for which the superactivation is possible.     

Measurement-based quantum correlation in mixed-state quantum metrology

Entanglement is crucial for realizing quantum advantages in metrology. However, entanglement has been outcast by discord in order to capture the worst-case sensitivity in quantum metrology to estimate an unknown parameter. In contrast to traditional measures—namely entanglement and discord—there exist noncommutativity-based quantum correlation measures induced by local von Neumann measurements. Such correlations are more comprehensive than entanglement and discord in quantum information processing. In this paper, we investigate the metrological resourcefulness of measurement-based quantum correlations (MbQCs). We provide a lower bound on the minimum precision of the estimation in terms of the MbQC. We show that the MbQC is more resourceful in quantum metrology than entanglement and super quantum discord. For any non-product state, the MbQC gives a metrological insight into the sensitivity of a mixed state toward perturbation caused by a local von Neumann measurement.     

Protecting quantum entanglement and correlation by local filtering operations

In this work, the protection of different quantum entanglement and correlation is explored by local filtering operations. The results show that the filtering operations can indeed be useful for combating amplitude-damping decoherence and recovering the quantum entanglement and correlation. In this scheme, although the final states satisfy the quantum entanglement and correlation, the corresponding initial noisy states does not satisfy them, which means that the filtering operations can reveal the hidden genuine quantum entanglement and correlation of these initial noisy states.     

Quantum correlation via quantum coherence

Quantum correlation includes quantum entanglement and quantum discord. Both entanglement and discord have a common necessary condition—quantum coherence or quantum superposition. In this paper, we attempt to give an alternative understanding of how quantum correlation is related to quantum coherence. We divide the coherence of a quantum state into several classes and find the complete coincidence between geometric (symmetric and asymmetric) quantum discords and some particular classes of quantum coherence. We propose a revised measure for total coherence and find that this measure can lead to a symmetric version of geometric quantum correlation, which is analytic for two qubits. In particular, this measure can also arrive at a monogamy equality on the distribution of quantum coherence. Finally, we also quantify a remaining type of quantum coherence and find that for two qubits, it is directly connected with quantum nonlocality.     

Revealing halogen bonding interactions with anomeric systems: An ab initio quantum chemical studies

A computational study has been performed using MP2 and CCSD(T) methods on a series of O⋯X (X = Br, Cl and I) halogen bonds to evaluate the strength and characteristic of such highly directional noncovalent interactions. The study has been carried out on a series of dimeric complexes formed between interhalogen compounds (such as BrF, BrCl and BrI) and oxygen containing electron donor molecule. The existence and consequences of the anomeric effect of the electron donor molecule has also been investigated through an exploration of halogen bonding interactions in this halogen bonded complexes. The ab initio quantum chemical calculations have been employed to study both the nature and directionality of the halogen molecules toward the sp³ oxygen atom in anomeric systems. The presence of anomeric n_O → σ*_CN interaction involves a dominant role for the availability of the axial and equatorial lone pairs of donor O atom to participate with interhalogen compounds in the halogen-bonded complexes. The energy difference between the axial and equatorial conformers with interhalogen compounds reaches up to 4.60 kJ/mol, which however depends upon the interacting halogen atoms and its attaching atoms. The energy decomposition analysis further suggests that the total halogen bond interaction energies are mainly contributed by the attractive electrostatic and dispersion components. The role of substituents attached with the halogen atoms has also been evaluated in this study. With the increase of halogen atom size and the positive nature of σ-hole, the halogen atom interacted more with the electron donor atom and the electrostatic contribution to the total interaction energy enhances appreciably. Further, noncovalent interaction (NCI) studies have been carried out to locate the noncovalent halogen bonding interactions in real space.     

Mediating and inducing quantum correlation between two separated qubits by one-dimensional plasmonic waveguide

We investigate the dynamics of quantum correlation between two separated qubits trapped in one-dimensional plasmonic waveguide. It is found that for a class of initial states, the quantum discord shows a sudden change phenomenon during the dynamical evolution. Furthermore, we demonstrate that the quantum discord can be enhanced if a proper product of the plasmon wave number and two qubits distance is chosen. Finally, we find that the non-zero quantum discord between two qubits can be created for the states without initial quantum discord during the time evolution of the system.     

Quantum Fisher information,quantum entanglement and correlation close to quantum critical phenomena

In this paper, we investigate the quantum Fisher information (QFI), quantum entanglement, quantum correlation and quantum phase transition (QPT) within the one-dimensional transverse Ising model by exploiting quantum renormalization-group method. The results show that quantum Fisher information, quantum entanglement, quantum correlation can evolve to two saturated values which exhibit QPT at the critical point after several iterations of the renormalization. Meanwhile, we find quantum entanglement or correlation can be detected perfectly by means of quantum Fisher information. Besides, it cannot capture any information about the system in the paramagnetic phase in view of quantum entanglement and correlation. Contrarily, it is evident the QFI is always nonzero even if the system is in the paramagnetic phase, i.e., the QFI can also be utilized as a highly favorable measure of quantum information in a broad of quantum spin systems. Furthermore, we disclose the nonanalytic and scaling behaviors of quantum Fisher information, which can be taken as a representation of quantum critical characterism.     

Study of quantum correlation swapping with relative entropy methods

To generate long-distance shared quantum correlations (QCs) for information processing in future quantum networks, recently we proposed the concept of QC repeater and its kernel technique named QC swapping. Besides, we extensively studied the QC swapping between two simple QC resources (i.e., a pair of Werner states) with four different methods to quantify QCs (Xie et al. in Quantum Inf Process 14:653–679, 2015). In this paper, we continue to treat the same issue by employing other three different methods associated with relative entropies, i.e., the MPSVW method (Modi et al. in Phys Rev Lett 104:080501, 2010), the Zhang method (arXiv:1011.4333 [quant-ph]) and the RS method (Rulli and Sarandy in Phys Rev A 84:042109, 2011). We first derive analytic expressions of all QCs which occur during the swapping process and then reveal their properties about monotonicity and threshold. Importantly, we find that a long-distance shared QC can be generated from two short-distance ones via QC swapping indeed. In addition, we simply compare our present results with our previous ones.     

量子系统动态函数的跟踪控制

以随时间变化的二次函数为目标函数,对采用薛定谔方程的量子系统进行轨迹跟踪研究。根据Lyapunov稳定性定理,选择误差的平方作为Lyapunov函数设计控制律,实现系统从任意初始状态到目标函数的跟踪。在Matlab环境下对不同初始状态进行了系统仿真及性能对比研究,分析了系统初始值以及控制中观测量对跟踪性能的影响,验证了控制律在跟踪目标函数上的优越性。     

Revealing the structure of hormonal regulation of enzymes by the pattern recognition method

The results of cluster data analysis are discussed with a view to revealing the structure of hormonal regulation of the activity of carbohydrate-lipid metabolism enzymes in white adipose tissue under stress conditions. The results, represented as a dendrogram, reflect the hierarchical structure of hormonal regulation of enzymes and stress adaptation syndrome (SAS) and are interpreted according to the logic of biochemical data. The problem is focused on the methodical aspects of the analysis of asymmetric relations on a set of objects with incomplete data. Yurii Filippovich Zuev. Born 1943. Graduated from the Latvian State University, in 1972. Currently is a researcher at the Il’ichev Pacific Institute of Oceanology. Scientific interests: biochemistry, biophysics, system analysis of the regulation of biological processes at the biochemical level, philosophical and biological problems of hierarchical relativity. Author of five papers in journals. Member of Biochemical Society.     

Distortion in the acousto-optic Wigner processor

The possibility of the creation of a compact optic Wigner processor is considered. The influence of distortions on the output signal, that appear in such an arrangement, is analyzed theoretically, experimentally and with the help of the mathematical simulation. It is shown that at practically used signal parameters these distortions in the Wigner distributions are not of great importance.     

Quantum correlation and quantum phase transition in the one-dimensional extended Ising model

Quantum phase transitions can be understood in terms of Landau’s symmetry-breaking theory. Following the discovery of the quantum Hall effect, a new kind of quantum phase can be classified according to topological rather than local order parameters. Both phases coexist for a class of exactly solvable quantum Ising models, for which the ground state energy density corresponds to a loop in a two-dimensional auxiliary space. Motivated by this we study quantum correlations, measured by entanglement and quantum discord, and critical behavior seen in the one-dimensional extended Ising model with short-range interaction. We show that the quantum discord exhibits distinctive behaviors when the system experiences different topological quantum phases denoted by different topological numbers. Quantum discords capability to detect a topological quantum phase transition is more reliable than that of entanglement at both zero and finite temperatures. In addition, by analyzing the divergent behaviors of quantum discord at the critical points, we find that the quantum phase transitions driven by different parameters of the model can also display distinctive critical behaviors, which provides a scheme to detect the topological quantum phase transition in practice.     

Revealing correlation patterns of individual location activity motifs between workdays and day-offs using massive mobile phone data

Recently, people are increasingly interested in understanding broader and longer-term individual activity-travel behaviors across days or even weeks. However, the relationship of individual daily activity-travel behaviors over multi-days only remains partially revealed, especially between workdays and day-offs. Thus, we develop an effective framework to extract individual daily activity-travel patterns from massive mobile phone network data on basis of location activity motifs (LAMs), which are beneficial to combining the locations, activities, and trips in daily activity-travel behaviors. We then discover that the modified number of LAMs over time conforms well to the classic exploration and preferential return (EPR) model after excluding the influence of the number of trips, which reproduces the human activity-travel behavior characteristics on daily scale and indicates that the complex relationship of LAMs exists between workdays and day-offs. Furthermore, we emphasize three categories of correlation patterns while the relationship of LAMs between workdays and day-offs is instantiated using association rules mining algorithm. Ultimately, the regular individual differences and obvious spatial heterogeneity reveal the formation mechanism of correlation patterns. These empirical results contribute to develop different but related transportation strategies between workdays and day-offs by understanding individual daily activity-travel behaviors.     

On the Reliability of Computing Wigner Texture Features

In this work we analyse the robustness of the computation of pseudo-Wigner texture features using both analytic and statistical methods. It is shown that if the input error is normally distributed and the SNR of the input is not very low (i.e. if SNR 3), then the output error is also normally distributed with known mean and variance. The error distribution in some typical simple signals is considered. The effects of quantisation are also investigated.     

Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities

Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.