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Quantum coherence and quantum steering are extremely useful resources for quantum information technology. Based on the correlation between quantum coherence and quantum steering, the steered quantum coherence (SQC) is formed, which is a new quantum correlation measurement method. In this paper, the SQC is applied to explore the dynamic evolution of quantum correlation in non-Markovian systems and it is also compared with typical quantum entanglement (QE). The results show that same as the QE, the SQC can also measure the quantum correlation of quantum system. Further research shows that there are obvious differences between the two measurement methods: on the one hand, in the process of non-Markovian dynamics evolution, death and rebirth occur for QE, but not for SQC, which indicates that SQC is more robust than QE; on the other hand, the superposition effect of the channel is not conducive to maintaining the QE of the system, but it is beneficial to maintaining the SQC. [ABSTRACT FROM AUTHOR]

Special fermionic systems entered the realm of quantum chemistry in the seventies in the work of Borland and Dennis in the form of a toy model. This work was leading to a detailed study of the N-representability problem by Klyachko. The topic then has been reconsidered in the light of entanglement theory boiling down to the notion of entanglement polytopes. Recently building on certain properties of such special fermionic systems, a connection between the coupled cluster method and entanglement has been established. In this paper we show that precisely such a special class of systems also provides an interesting physical realization for structures related to the Lie algebras of exceptional groups. This result draws such exotic symmetry structures under the umbrella of entangled systems of physical relevance. [ABSTRACT FROM AUTHOR]

A salient merit of processing quantum information is the ability of simultaneously working with both bit zero and bit one. The basic unit of quantum information, the so-called qubit, is a superposition of two orthogonal (or near-orthogonal) quantum states which can be realised on distinct physical platforms. At present, no unique qubit encoding exists that is superior to all the other ones. Different labs are implementing their most convenient technique for encoding the qubit and so the network of labs becomes heterogeneous. In this paper, we consider two types of qubit encodings, one is the single-rail qubit in terms of discrete-variable (DV) states 0 and 1 which are respectively the vacuum and the single-photon state and the other is the coherent-state qubit in terms of continuous-variable (CV) states α and - α which are coherent states with equal amplitudes but opposite phases. We devise linear-optics schemes to teleport one type of qubit to the other type. More than that, our teleportation schemes are designed so that two kinds of controllers, one is capable of manipulating single-rail qubits (DV controller) while the other coherent-state ones (CV controller), are able to simultaneously supervise the tasks in both directions. We first propose a quantum circuit to prepare a relevant four-party pure entangled state serving as a quantum channel between the four participants: two teleporters and two controllers. We then detail the hybrid controlled teleportation protocols taking into account the dissipation effect caused by the presence of losses in the environment surrounding the participants. [ABSTRACT FROM AUTHOR]

We investigate how the efficiency is affected on the noise environments in the controlled remote state preparation protocol, where the several realistic scenarios, i.e., a part or all of the qubits are subjected to the same or different types of noise, are considered. We find that more noise or less entanglement of qubits environment lead to more efficiency in terms of average fidelity. We show that it is better way to subject the qubits in different noise channels in order to increase the fidelity of the controlled remote state preparation protocol. By using a non-maximally three-qubit pure entangled state as quantum channel, furthermore, we could realize a perfect controlled remote state preparation by choosing the right noisy environments and adjusting their relations in terms of noisy rates. [ABSTRACT FROM AUTHOR]

In this paper we consider the situation that four identical two-level atoms are separately trapped in four single-mode optical cavities, which are placed at the vertices of a tetrahedron and coupled by six fibers. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the schrödinger equation when the total excitation number of the system equals one. The geometrical quantum discords between atoms and between cavities are investigated. The effects of cavity-fiber coupling coefficient on the geometrical quantum discords between atoms and between cavities are discussed. The results obtained using the numerical method indicate that the geometrical quantum discords between atoms and between cavities are all weakened with increase of cavity-fiber coupling coefficient. [ABSTRACT FROM AUTHOR]

In a recent article in this journal Guo-Hui (Int. J. Theor. Phys. 56, 600, 2017) has investigated the quantum correlation properties in the two qubits one-axis spin squeezing model with an external magnetic field by means of concurrence (C) and quantum discord (QD) criteria. We are to reveal numerically and analytically that in the limiting case T→ 0 (ground state) the sudden disappearance phenomenon (SDP) does not occur in the behavior of C and the values obtained for C are incorrect. [ABSTRACT FROM AUTHOR]

In this paper, we consider the situation that four identical two-level atoms are separately trapped in separated tetrahedral structure single-mode optical cavities, which are placed at the vertices of a tetrahedron and are coupled by four fibres. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the Schrödinger equation when the total excitation number of the system equals one. Negativity is adopted to quantify the degree of entanglement between two subsystems. The entanglement dynamics between atoms and between cavities is studied. The influences of atom-cavity coupling coefficient on the entanglement between atoms and that between cavities are discussed. The results obtained using the numerical method show that the atom-atom entanglement and the cavity-cavity entanglement are all strengthened with increase of atom-cavity coupling coefficient. [ABSTRACT FROM AUTHOR]

We introduce local filters as a means to detect the entanglement of bound entangled states which do not yield to detection by witnesses based on positive maps which are not completely positive. We demonstrate how such non-detectable bound entangled states can be locally filtered into detectable bound entangled states. Specifically, we show that a bound entangled state in the orthogonal complement of the unextendible product bases (UPB), can be locally filtered into another bound entangled state that is detectable by the Choi map. We reinterpret these filters as local measurements on locally extended Hilbert spaces. We give explicit constructions of a measurement-based implementation of these filters for $$2 \otimes 2$$ and $$3 \otimes 3$$ systems. This provides us with a physical mechanism to implement such local filters. [ABSTRACT FROM AUTHOR]

The entanglement evolution of a mixed three-qubit W-type state in three independent non-Markovian reservoirs with Lorentzian spectral density is investigated. The effects of the non-Markovianity of environment, initial state and the detuning on the entanglement dynamics in three-qubit system are presented. The results show that the entanglement between qubits in many-body system is more complicated than that in two-body system. First, the disentanglement criterion for two qubits is not suitable for multi qubits. Second, in many-body system, the effects of weight number characterizing the initial state distribution on the entanglement between two arbitrary qubits may be opposite. Further numerical calculations show that increasing the amount of non-Markovianity λ / γ , the purity of the initial quantum state or the detuning are all conducive to maintain the entanglement between qubits. [ABSTRACT FROM AUTHOR]

We investigate the relation between dissipation and coherent effects in the dynamics of quantum entanglement (QE) between two qubits by means of weak measurement. Under weak measurement, the increase or decrease of QE closely relates with the dissipation. The amplitude of QE will only be elevated through enhancing the measurement strength in weak correlated or no correlated instantaneous modes, and the entanglement sudden death (ESD) is retarded effectively. In the correlated dephasing mode, however, the amplitude of QE will decrease due to the increases of measurement strength. The periods for entanglement death, as well as the dark and bright in the concurrence are not changed. Therefore, the environmental relevance helps to enhance the amplitude of QE and delay the entanglement death. [ABSTRACT FROM AUTHOR]

A scheme is proposed to prepare W -type entangled squeezed vacuum states (ESVSs) via free-travelling optical fields with simple linear optical devices, photo detectors and cross-Kerr medium. We investigate the influence of an inexact nonlinear phase factor between two modes on the fidelity of the prepared three-mode W -type ESVSs. By adjusting the appropriate reflectivity, the scheme can be extended to create 2 n + 1 -mode W -type ESVSs. [ABSTRACT FROM AUTHOR]

Some properties of three-qubit systems interacting with a noisy environment are discussed. The amount of the survival entanglement is quantified for the Greenberger-Horne-Zeilinger (GHZ) and W states. It is shown that the entanglement decay depends on the noise type (correlated or non-correlated), the number of interacting qubits with the environment, and the initial state that passes through this noisy environment. In general, the GHZ state is more fragile than the W state. The phenomenon of entanglement sudden death appears in the GHZ state only for non-correlated noise. [ABSTRACT FROM AUTHOR]

We propose two schemes to generate GHZ-type and W-type entangled squeezed vacuum states with free-travelling optical fields via a single-photon source, the Kerr medium, balanced beam-splitters and single-photon detectors. The effects of a fluctuation of nonlinear phase shift between two optical fields on the fidelity and on the success probability are discussed. We also discuss the effects of the imperfection of photon detectors on the success probability and the experimental feasibility of the present schemes. [ABSTRACT FROM AUTHOR]

Quantum information technology largely relies on a sophisticated and fragile resource, called quantum entanglement, which exhibits a highly nontrivial manifestation of the coherent superposition of the states of composite quantum systems. In this paper, we study the interaction between the general and even coherent fields with moving and stationary two two-level atoms. In this regard, this paper investigates the von Neumann entropy and the atoms-field tangle as a measure of entanglement between the general and even coherent fields with the two atoms. Also, the entanglement between the two atoms using concurrence and negativity during time evolution is discussed. This paper examines the effects of multiphoton transitions and initial state setting on the entanglement for the system under consideration. Finally, the results demonstrate an important phenomenon such as the sudden death and birth of entanglement when the two atoms are initially in entangled states. [ABSTRACT FROM AUTHOR]

We set up the fermionic thermal entangled state approach to address Fermi operator master equations for the amplitude- and phase-decay processes and find the explicit Kraus operator-sum representations (KOSR) describing time-evolution of Fermi systems. As an application of KOSR, the evolution law of the two-level atomic system interacting with a photon field in these two decay processes is analytically derived, which shows that the interaction system has a quantum jump as a result of dissipation, but it always remains unchanged in the phase-decay process. [ABSTRACT FROM AUTHOR]

Quantum entanglement between two qubits was obtained by solving the model of two qubits coupled to two independent reservoirs. This paper studied the influences of dissipative environment, detuning between transition frequency of the qubit and center frequency of a cavity. Results showed that: (1) In the non-Markovian channel, a certain amount of detuning was conducive to maintain and improve the entanglement of a system. (2) On the other hand, in a two-sided amplitude damping channel, the composite effect of two independent dissipative channels would appear through the entanglement between two qubits. Given the composite effect of two independent channels, the entanglement dynamics not only affected the Markovian process but also hindered the backflow effect of the non-Markovian channel, which was not conducive to maintain the entanglement between qubits. [ABSTRACT FROM AUTHOR]

In this paper, we study how to fuse two W states into a larger W state in a cavity quantum electrodynamic system. Two atoms are collided within a detuned vacuum cavity mode. One atom is from the first N-atom W state system, and the other is from the second M-atom W state system. The two atoms will be detected after flying out of the cavity mode. If only one excitation is detected between the two atoms, an ( N + M − 2)-atom W state can be generated with some probability. If no excitation is detected between the two atoms, the remaining ( N − 1)-atom W state and ( M − 1)-atom W state can be re-fused using the same procedure, continuing until two excitations are detected between the two atoms. Using this procedure, the chance of entanglement of the two W states is as large as possible. A feasibility analysis indicates that this scheme can be implemented using existing experimental technologies. [ABSTRACT FROM AUTHOR]

We present two deterministic entanglement purifications protocols for χ-type entangled states, resorting to multiple degrees of freedom. One protocol is implemented with the spatial entanglement to distill the maximally entangled states from the mixed states, resorting to some linear optical elements. Another one is implemented with the frequency entanglement for the purification. All the parties can jointly distill the maximally entangled states from the mixed states affected by the environmental noise during transmission. Both of the protocols can work in a deterministic way with the success probability 100 %, in principle. The derived features may make the protocols useful in the practical long-distance quantum communication. [ABSTRACT FROM AUTHOR]

We present criteria to detect the depth of entanglement in macroscopic ensembles of spin- j particles using the variance and second moments of the collective spin components. The class of states detected goes beyond traditional spin-squeezed states by including Dicke states and other unpolarized states. The criteria derived are easy to evaluate numerically even for systems of very many particles and outperform past approaches, especially in practical situations where noise is present. We also derive analytic lower bounds based on the linearization of our criteria, which make it possible to define spin-squeezing parameters for Dicke states. In addition, we obtain spin squeezing parameters also from the condition derived in (Sørensen and Mølmer 2001 Phys. Rev. Lett. https://doi.org/10.1103/physrevlett.86.4431 86 https://doi.org/10.1103/physrevlett.86.4431 ). We also extend our results to systems with fluctuating number of particles.

The unitary equivalence of different bipartite entangled states with continuous variables under unitary transformations are investigated. With the help of the technique of integration within an ordered product of operators, the corresponding unitary operators are also derived. These results may deepen people's understanding to the various bipartite entangled states, and enrich the representations and transformations theory in quantum mechanics. [ABSTRACT FROM AUTHOR]

We discuss aspects of entanglement and quantum discord, two of the quantum correlations that are of much interest in the field of quantum information. Their definitions and handling will be discussed, with simple illustrative examples. A specific example is of entanglement decay resulting from a simple dissipative process and how to alter that decay. An analytical prescription for computing quantum discord when a qubit (spin-1/2 or two-level quantum system) is involved is presented along with applications, and its generalization to higher spins (many levels) indicated. [ABSTRACT FROM AUTHOR]

Our work addresses the problem ofgenerating maximally entangled two spin-1/2 (qubit) symmetric states using NMR, NQR, Lipkin-Meshkov-Glick Hamiltonians. Time evolution of such Hamiltonians provides various logic gates which can be used for quantum processing tasks. Pairs of spin-1/2s have modelled a wide range of problems in physics. Here, we are interested in two spin-1/2 symmetric states which belong to a subspace spanned by the angular momentum basis {| j = 1, μ〉; μ = + 1, 0, −1}. Our technique relies on the decomposition of a Hamiltonian in terms of SU(3) basis matrices. In this context, we define a set of linearly independent, traceless, Hermitian operators which provides an alternate set of SU( n) generators. These matrices are constructed out of angular momentum operators J, J, J. We construct and study the properties of perfect entanglers acting on a symmetric subspace, i.e., spin-1 operators that can generate maximally entangled states from some suitably chosen initial separable states in terms of their entangling power. [ABSTRACT FROM AUTHOR]

Abstract: The paper investigates the dynamic evolution behaviors of entanglement and quantum discord of coupled superconducting qubits in circuit QED system. We put emphasis on the effects of cavity field quantum state on quantum entanglement and quantum correlations dynamic behaviors of coupling superconducting qubits. The results show that, (1) generally speaking, the entanglement will appear the death and new birth because of the interaction between qubits and cavity field, on the contrary, this phenomenon will not appear in quantum discord. (2) When the cavity field is in coherent state, the entanglement survival time is controlled by the average photon number. The more the average photon number is, the longer survival time of entanglement is prolonged. Thus it has the benefit of keeping quantum correlations. (3) When the cavity field is in squeezed state, the squeezed amplitude parameters have controlling effects on quantum correlations including entanglement and quantum discord. On the one hand, the increase of squeezed amplitude parameters can prolong the survival time of entanglement, on the other hand, with the increase of squeezed amplitude parameters, the robustness of quantum discord is more and more superior to concurrence and is more advantage to keep the system quantum correlations. The further study results show that the increase of the initial relative phase of coupling superconducting qubits can also keep the quantum correlations. [Copyright &y& Elsevier]

Abstract: By using geometric quantum discord and measurement-induced nonlocality, quantum correlations are investigated for two superconducting (SC) charge qubits that share a large Josephson junction where the field is assumed to be prepared initially in a coherent state. It is found that the difference between measure measurement-induced nonlocality and geometric quantum discord, of the final state of the two SC-charge qubits system which is especial case of X-states, is equal to a constant value. It is found that the quantum correlations and entanglement of the qubits are very sensitive to the mean number of the coherent photons. The entanglement exists in small intervals of death quantum discord and measurement-induced nonlocality. This is further evidence in support of the fact that quantum correlation and entanglement are not synonymous. [Copyright &y& Elsevier]

Abstract: In the presence of degenerate two-photon transitions the problem of the interaction between two two-level atoms and a single-mode is considered. Near resonance case, a closed form of the analytic solution for the wave function is obtained. The entanglement between an atom and field in the interacting system is studied by using the change in atomic and field entropies. The relationship between entropy changes and concurrence entanglement is discussed. Our results show that the behavior of the entropy change in agreement with the behavior of the concurrence to measure the entanglement between two subsystem structures. [Copyright &y& Elsevier]

Abstract: Utilizing the concurrence and the quantum discord as the measure method, in this paper we compare and investigate the dynamic evolution features of quantum correlations of coupled qubits in non-Markovian process. We focus attention on decoherence effect influences the stability of quantum correlations. The investigation results show that because of the decoherence influence between the system and environment, the concurrence always evolves with time in oscillation form in the way of deaths and survivals, however, the quantum discord time evolution does not appear the deaths and survivals. The quantum discord survives obviously longer than concurrence, which indicates that quantum discord has a stronger ability to resist decoherence than entanglement. Through regulating and controlling the purity and entanglement of the initial quantum state, we can effectively suppress the decay of the quantum correlations, which is advantaged to complete the quantum information processing. [Copyright &y& Elsevier]

Abstract: We construct a tripartite entangled sate representation in Fock space, which is the eigenstate of the three compatible operators (Q 1 − Q 3), (Q 1 + Q 2 + Q 3) and (P 1 −2P 2 + P 3). Using the technique of integration within an ordered product (IWOP) of operators, we show that |p, χ 1, χ 2〉 are complete and orthogonal, and hereby qualified for making up a quantum mechanical representation. Its squeezing property is explored and an optical device for producing this three-mode entangled state are proposed. [Copyright &y& Elsevier]

Abstract: Utilizing the concurrence and the Bell inequality, we investigated in detail the evolution of entangled decoherence of two superconductor qubits in non-Markovian process. The results show that the evolution of entanglement dynamics can cause entanglement sudden death (ESD) and entanglement sudden birth (ESB) because of the interaction between the environment and the quantum qubits. The concurrence of a quantum system is not only related with the environmental dissipation effects, the interaction between the qubits, and the initial quantum state, but also strongly related with the coupling symmetry between qubit-environment. Under certain initial states, the effect of environmental dissipation can be avoided completely by controlling the coupling model between qubits and environments. The interaction between qubits can prolong the survival time of the entanglement, and it is the dynamic for reviving the entanglement of quantum system. The further research results indicate that, the non-Markovian memory effects of the environment are helpful to prolong the survival time of the entanglement or to prevent the outbreak of ESD. [Copyright &y& Elsevier]

Abstract: The exact solution of the problem of two two-level atoms interacting with a two-mode radiation field in the presence of a parametric converter term is presented. More precisely we have considered a Hamiltonian model that includes two types of interaction: one is the field–field (frequency converter type) and the other is the atom–field interaction. By introducing a canonical transformation an exact solution of the wave function in the Schrödinger picture is obtained. The result presented in this context is used to discuss the atomic inversion as well as the entropy squeezing and variance squeezing phenomena. We use the von Neuman entropy to measure the degree of entanglement between the atom and the field. These aspects are sensitive to changes in the converter parameter. [Copyright &y& Elsevier]

We present a novel study of the time evolutions of entangled states of three spin-1/2 particles in the presence of a constant external magnetic field, which causes the individual spins to precess and leads to remarkable periodicities in the correlations and density matrices. The emerging patterns of periodicity are studied explicitly for different entangled states and in detail for a particular initial configuration of the velocities. Contributions to precession of anomalous magnetic moments are analysed and general results are also obtained. We then introduce an electric field orthogonal to the magnetic field, linking to the preceding case via a suitable Lorentz transformation, and obtain the corresponding Wigner rotations of the spin states. Finally, we point out for the first time that the entangled states corresponding to well-known ones in the study of 3-particle entanglements, may be classified systematically using a particular coupling of three angular momenta. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the entanglement of the three modes of radiation field interacting with moving two-level atom. The time evolution of the von Neumann entropy, entropy squeezing and marginal atomic Q-function is investigated. The marginal atomic Q-function as an indicator of the squeezing and entanglement of the system is suggested. The results highlight the important roles played by both the atomic motion parameter and intial atomic position in determining the evolution of the quantum entanglement, entropy squeezing and marginal atomic Q-function. The new phenomena of entanglement sudden death and sudden birth can be obtained using special values of the number of photon transition and atomic motion parameter. We demonstrate the connections between von Neumann entropy, entropy squeezing and marginal atomic Q-function. [ABSTRACT FROM AUTHOR]

A simple one-dimensional model for the system-apparatus interaction is analysed. The system is a spin-1/2 particle, and its position and momentum degrees constitute the apparatus. An analysis involving only unitary Schrödinger dynamics illustrates the nature of the correlations established in the system-apparatus entangled state. It is shown that even in the absence of any environment-induced decoherence, or any other measurement model, certain initial states of the apparatus - like localized Gaussian wavepackets - are preferred over others, in terms of measurementlike one-to-one correlations in the pure system-apparatus entangled state. [ABSTRACT FROM AUTHOR]

Some Hamiltonians are constructed from the unitary $${\check{R}_{i,i+1}(\theta, \varphi)}$$-matrices, where θ and $${\varphi}$$ are time-independent parameters. We show that the entanglement sudden death (ESD) can happen in these closed Yang–Baxter systems. It is found that the ESD is not only sensitive to the initial condition, but also has a great connection with different Yang–Baxter systems. Especially, we find that the meaningful parameter $${\varphi}$$ has a great influence on ESD. [ABSTRACT FROM AUTHOR]

Abstract: The fixed-trace ensemble of random complex matrices is the fundamental model that excellently describes the entanglement in the quantum states realized in a coupled system by its strongly chaotic dynamical evolution [see H. Kubotani, S. Adachi, M. Toda, Phys. Rev. Lett. 100 (2008) 240501]. The fixed-trace ensemble fully takes into account the conservation of probability for quantum states. The present paper derives for the first time the exact analytical formula of the one-body distribution function of singular values of random complex matrices in the fixed-trace ensemble. The distribution function of singular values (i.e. Schmidt eigenvalues) of a quantum state is so important since it describes characteristics of the entanglement in the state. The derivation of the exact analytical formula utilizes two recent achievements in mathematics, which appeared in 1990s. The first is the Kaneko theory that extends the famous Selberg integral by inserting a hypergeometric type weight factor into the integrand to obtain an analytical formula for the extended integral. The second is the Petkovšek–Wilf–Zeilberger theory that calculates definite hypergeometric sums in a closed form. [Copyright &y& Elsevier]

Abstract: We theoretically show that the process of inner-shell photoionization in an atom A, followed by the spontaneous sequential emission of two Auger electrons, produces various kinds of spin-entangled states of three flying electronic qubits. All properties of these states are completely pre-determined by the total spin quantum numbers of the electronic states of four atomic species (i.e., A, , , ) participating in this process in the Russell–Saunders coupling. These tripartite states are readily characterized experimentally by measuring only energies of the three emitted electrons, without requiring any entanglement witness or other such protocols. [Copyright &y& Elsevier]

Abstract: We study a single Cooper pair box interacting with a single cavity mode and discuss the roles played by the detuning parameters and charged capacities on the degree of entanglement. For large values of the detuning parameter the survival of the entanglement is increased. We generate a maximum entangled state and use it to perform the original teleportation protocol. The fidelity of the teleportated state is increased due to decrease in the detuning parameter and the number of photon inside the cavity. [Copyright &y& Elsevier]

Abstract: We apply the continuous-variable quantization scheme to quantize public goods game and find that new pure strategy Nash equilibria emerge in the static case. Furthermore, in the evolutionary public goods game, entanglement can also contribute to the persistence of cooperation under various population structures without altruism, voluntary participation, and punishment. [Copyright &y& Elsevier]

Abstract: We study the squeezing and pairwise entanglement properties of multi-qubit spin systems, implemented by a two-axis countertwisting Hamiltonian, with and without an external field. We show that the addition of an external field, enforces stronger squeezing and entanglement, and also increases the time duration that these phenomena may be maintained. [Copyright &y& Elsevier]

We investigate the geometrical structure of entangled and separable bipartite and multipartite states based on the secant variety of the Segre variety. We show that the Segre variety coincides with the space of separable multipartite state and the higher secant variety of the Segre variety coincides with the space of entangled multipartite states. [ABSTRACT FROM AUTHOR]

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distant particles. In an entangled EPR two-particle system, the value of the momentum (position) for neither single subsystem is determined. However, if one of the subsystems is measured to have a certain momentum (position), the other subsystem is determined to have a unique corresponding value, despite the distance between them. This peculiar behavior of an entangled quantum system has surprisingly been observed experimentally in two-photon temporal and spatial correlation measurements, such as “ghost” interference and “ghost” imaging. This article addresses the fundamental concerns behind these experimental observations and to explore the nonclassical nature of two-photon superposition by emphasizing the physics of 2 ≠ 1 + 1. [ABSTRACT FROM AUTHOR]

Abstract: Within the framework of constructions for quantifying entanglement, we build a natural scenario for the assembly of multipartite entanglement measures based on Hopf bundle-like mappings obtained through Clifford algebra representations. Then, given the non-factorizability of an arbitrary two-qubit density matrix, we give an alternate quantity that allows the construction of two types of entanglement measures based on their arithmetical and geometrical averages over all pairs of qubits in a register of size N, and thus fully characterize its degree and type of entanglement. We find that such an arithmetical average is both additive and strongly super additive. [Copyright &y& Elsevier]

Abstract: It is shown that the atom–field interaction, in the context of the Jaynes–Cummings model, leads periodically to a Schmidt decomposition of the atom–field state at times within the first collapse region. For some initial average photon number maximally entangled atom–field state are generated. [Copyright &y& Elsevier]

Abstract: We investigate quantum correlations of the N-qubit states via a collective pseudo-spin interaction on arbitrary pure separable states for a given interval of time. Based on this dynamical generation of the N-qubit maximal entangled states, a quantum secret sharing protocol with N continuous classical secrets is developed. [Copyright &y& Elsevier]

The unitary braiding operators describing topological entanglements can be viewed as universal quantum gates for quantum computation. With the help of the Brylinski’s theorem, the unitary solutions of the quantum Yang–Baxter equation can be also related to universal quantum gates. This paper derives the unitary solutions of the quantum Yang–Baxter equation via Yang–Baxterization from the solutions of the braid relation. We study Yang–Baxterizations of the non-standard and standard representations of the six-vertex model and the complete solutions of the non-vanishing eight-vertex model. We construct Hamiltonians responsible for the time-evolution of the unitary braiding operators which lead to the Schrödinger equations. [ABSTRACT FROM AUTHOR]

Abstract: We discuss a general formalism for the inference of quantum density operators from incomplete information, based on the maximization of general non-additive entropic forms, and its application to the reconstruction of mixed states of composite quantum systems from generalized Bell measurements. The method provides a direct way to infer least biased densities with minimum entanglement for any data determined by Bell constraints in two qubit systems, in contrast with the conventional scheme based on the von Neumann entropy. In particular, it is shown that in this case fake entanglement is always avoided for large q when the Tsallis entropy is employed. [Copyright &y& Elsevier]