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As astounding as it may still seem to many, Bell’s theorems do not prove nonlocality. Non separable multipartite objects exist classically, meaning with local physics, the statistical state measurement of which violates the famous inequalities. Alleviating the almost century old confusion, the correct laws of statistics and logic pinpoint the true oddity of quantum objects: duality. As it is shown in the first part of this short essay, duality plus conservation laws allow the violation of Bell’s inequalities for any spatio-temporal separation. To dig deeper into particle dualism, in the second part, a class of models is proposed as a working framework. It encompasses some chaotic excitable reaction-diffusion systems, whose generalized susceptibilities make them compatible with quantized fields and excitations, of any desired symmetry group including the renormalization semigroup. Particles are supposed topological in nature. Bohr-Sommerfeld quantization takes place thanks to topological invariants stemming from densely dispersed defects generated by a multifractal background. Entanglement phenomenology arises because latent variables exist that are carried away, along with the moving particles that have interacted, and by which correlations are preserved. Conservation is assumed to be born in the phase, just as momentum is for instance. In other words, all known phenomena in physics are deterministic, classical and real, in the sense that information does propagate locally and experiments conducted statistically do hide latent variables. [ABSTRACT FROM AUTHOR]

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]

Quantum nonlocality is a very important quantum resource. Different types of quantum correlation can present the quantum nonlocality in varying degrees. In this paper, we investigate the dynamic evolution of steered quantum coherence (SQC) for a system of interacting qubits in contact with various models of the environment, and emphatically compare the robustness of SQC and quantum entanglement (QE). The results show that from the given initially state, due to the decoherence effect, both SQC and QE evolve with time in the form of oscillation. In the process of dynamic evolution, the QE will appear death and rebirth for all different decay modes. Differently, the SQC will not emerge the sudden death or the dark and bright, which shows a stronger robustness than QE. Moreover, we find that, under the long-term limit condition, the SQC will approach the steady value in different decay modes, which provides a reliable resource foundation for the completion of quantum information processing. [ABSTRACT FROM AUTHOR]

Bell non-locality and steering are archetypal characteristics of quantum mechanics that mark a significant departure from conventional classical notions. They basically refer to the presence of quantum correlations between separated systems which violate a non-local inequality, the violation otherwise is not possible if we restrict ourselves only to classical correlations. In view of the importance of such unique correlations, one may be interested to generate more states exhibiting non-locality starting from a few, a protocol which is termed as broadcasting. However, in the present submission, we show using universal Buzek–Hillary (BH) quantum cloning machine that, if one restricts to broadcasting through local quantum cloning, then such non-locality cannot be broadcasted. Our study is done in the purview of the Bell-CHSH inequality and the CJWR [E G Cavalcanti et al, Phys. Rev. A80, 032112 (2009)] steering inequality. It is observed that when the number of measurement settings is greater than 6, some of the output states are steerable after the application of local optimal BH cloners. We found that, under some restrictions, if the Werner and Bell diagonal states are subjected to such procedures, then the resultant state is rendered unsteerable. We extended this study to three qubit systems and found that genuine tripartite non-locality cannot be broadcasted using universal BH local quantum cloners, when the Svetlichny's inequality was considered. For two qubit systems, we considered 10 5 simulated general local unitaries over Werner and Bell-diagonal states and found that for none of these states, broadcasting on non-locality and 3-steerability is possible. [ABSTRACT FROM AUTHOR]

The remote state preparation (RSP) plays an important role in quantum information processing. In this study we present a scheme, where an eight-qubit entangled state is used as the quantum channel to prepare the four-qubit entangled state in a bidirectional manner. In this scheme, two distant parties, Alice and Bob are not only senders but also receivers, and Alice wants to assist Bob in remotely preparing a known four-qubit state, while Bob wants to assist Alice in remotely preparing a four-qubit state, respectively. We show that our scheme is deterministic, meaning that the bidirectional remote state preparation can have a 100% overall success probability. [ABSTRACT FROM AUTHOR]

An extended non-local field equations characterised by modified dispersion relations have been constructed based on non-local differential and hyperdifferential quantum operators. The dispersion relations obtained are found to be comparable to those obtained within the framework of unified theories and the covariant Kempf–Mangano algebra but free from tachyons. For the case of neutral meson, the upper limit of the characteristic length scale was found to be very close to the nuclear radius obtained from the study of β + -decay energy from finite-sized nuclei. [ABSTRACT FROM AUTHOR]

In this paper, a joint remote state preparation scheme for an arbitrary single-qutrit state is proposed. First, we introduce how to remotely prepare an arbitrary single-qutrit state in the ideal environment with the form of the density operator. Then we investigate the effects of four typical types of 3D Pauli-like noises corresponding to the Weyl operators: the trit-flip, the t-phase-flip, the trit-phase-flip and the t-depolarising in the ideal environment. For each type of noise, we calculate and analyse the results of fidelity. The results show that when the trit-flip, the trit-phase-flip and the t-depolarising noises are considered, the fidelity is related to the noise factor and all the coefficients of the target state. However, when the t-phase-flip noise is considered, the fidelity is only related to the noise factor and the amplitude coefficients of the target state. [ABSTRACT FROM AUTHOR]

Recently, Pan proposed a semi-quantum dialogue scheme with Bell entangled states Pan (Int. J. Theor. Phys. 59, 1364-1371, 2020). Here we re-examin the security of it and discover a security vulnerability in the original scheme. Eavesdropper Eve may utilize double controlled-not operation attack to obtain Bob’s secret without being detected. Finally, we give an improvement of the semi-quantum dialogue protocol and prove its security. We sincerely hope the researchers pay enough attention to double controlled-not operation attack hidden in semi-quantum cryptography protocols and design truly secure semi-quantum protocols. [ABSTRACT FROM AUTHOR]

In entanglement theory, the long-standing distillability problem asks whether the two-copy 4 × 4 Werner states are distillable under local operations and classical communications. We report the partial solution to the problem when the involved 4 × 4 matrices A and B, respectively, have one and three nonzero entries. As a corollary, the problem is solved when A and B have at most four nonzero entries. Our result presents the latest progress on the problem. [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]

Deformed Jaynes–Cummings model (JCM) has a physical importance in quantum optics. Hence, we investigated the nonlinear JCM including the intensity-dependent coupling constant and the additional Kerr term. The cavity was assumed to be in thermal equilibrium with a heat reservoir at temperature T. Using the generators of a closed algebra which reduces to the su(1, 1) and Heisenberg–Weyl algebras at limiting cases, and considering the total excitation number as a constant of motion, the total Hilbert space decomposes into two subspaces. So the eigenvalues and the corresponding eigenvectors were obtained. We derived the thermal density matrix and analysed the fidelity and thermal entanglement using negativity measure. Furthermore, we studied the Berry phase of the nonlinear atom–field system and explored the influence of nonlinearity on the quantum phase transition (QPT) point and entanglement. It is found that the deformation parameter can strongly affect the fidelity, negativity and QPT point. [ABSTRACT FROM AUTHOR]

By using the complete solution of the Milburn equation (beyond the Lindblad form that it is generally used) that describes intrinsic decoherence, we studied the decaying dynamics of a displaced harmonic oscillator. We calculated the expectation values of position quadrature and the number operator in the initial coherent and squeezed states. [ABSTRACT FROM AUTHOR]

Sequential sharing of nonlocal correlation is inherently related to its application. We address the question as to how many observers can share the nonlocal advantage of quantum coherence (NAQC) in a (d × d)-dimensional state, where d is a prime or a power of a prime. We first analyze the trade-off between disturbance and information gain of the general d-dimensional unsharp measurements. Then in a scenario where multiple Alices perform unsharp measurements on one party of the state sequentially and independently and a single Bob measures coherence of the conditional states on the other party, we show that at most one Alice can demonstrate NAQC with Bob. This limit holds even when considering the weak measurements with optimal pointer states. These results may shed light on the interplay between nonlocal correlations and quantum measurements on high-dimensional systems and the hierarchy of different quantum correlations. [ABSTRACT FROM AUTHOR]

Identification of quantum phase transitions has been a long standing issue in quantum systems. In this work, we study the renormalization of Wigner–Yanase skew information in XY spin chain and compare its relation with cost of energy quantum correlation near the critical point. This study is presented by implementing the quantum renormalization group (RG) technique. We apply the (RG) method to examine existing phase transition in XY spin chain by using the cost of energy quantum correlations and Wigner–Yanase skew information. We demonstrate that cost of energy quantum can provide crucial information about quantum phase transitions as well as quantum correlations. [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]

In this paper, the concept of nested multilevel entanglement is studied and formulated in terms of Matryoshka states. The generation of Matryoshka quantum resource states, which contain nested entanglement patterns, based on an anisotropic XY spin–spin interaction-based model has been proposed. Other classes of nested entanglement, such as in Matryoshka generalised GHZ states and Matryoshka Q-GHZ states, are studied. Generation, characterisation and application of a genuinely entangled seven-qubit resource state close to being a Matryoshka Q-GHZ states is explored, with theoretical schemes for quantum teleportation of arbitrary one-, two- and three-qubits states, bidirectional teleportation of arbitrary two-qubit states and probabilistic circular controlled teleportation proposed for the state. Fractal network protocols, surface codes and graph states as well as generation of arbitrary entangled states at remote locations are also discussed, to highlight the importance of this class of quantum states. [ABSTRACT FROM AUTHOR]

We uncover new behaviors of the transmission of information by three quantum channels in superposition of causal orders subject to some level of noise. We find that the transmission can exhibit three different behaviors as the level of noise is varied. This multifold behavior can be explained by the different equivalence classes of quantum switch matrices related to specific combinations of causal orders. We classify these matrices using their characteristic polynomials and matrix invariants, and we calculate analytical expressions for the Holevo information in three representative cases. Our results are a step forward to understand and harness quantum control of causal orders with different levels of noise. We also study the Holevo information as function of a continuous order parameter and analyze transitions at integer values. [ABSTRACT FROM AUTHOR]

We quantify the entanglement and its variations via generalized concurrence, Meyer–Wallach measure and its generalizations. Then we investigate the interactions between qubits on complete graphs, tree graphs, chain graphs and loop graphs with 3 to 8 qubits. It is observed that the amount of all entanglement measures in tree graph in the first group of considered graphs, are equal. The complete equivalent graph is equal and the entanglement measures for these graphs change altering the number of qubits. Furthermore, it can be seen that the entanglement measures are increased augmenting the number of qubits in the chain graph and loop graph. The entanglement of loop graphs is equal to or greater than the entanglement of chain graphs assuming the same number of qubits. Also there is a significant relation between entanglement, number of qubits, and interactions between qubits for the second group of considered graphs. As the number of interactions (presented by edges) increases between the qubits, the entanglements increase in these states. It is shown that the employed entanglement measures reveal the different values changing the number of qubits (vertices). [ABSTRACT FROM AUTHOR]

We study the entanglement and the Bell nonlocality of a coupled two-qubit system, in which each qubit is coupled with one individual environment. We study how the nonequilibrium environments (with different temperatures or chemical potentials) influence the entanglement and the Bell nonlocality. The nonequilibrium environments can have constructive effects on the entanglement and the Bell nonlocality. Nonequilibrium thermodynamic cost can sustain the thermal energy or particle current and enhance the entanglement and the Bell nonlocality. However, the nonequilibrium conditions (characterized by the temperature differences or the thermodynamic cost quantified by the entropy production rates) which give the maximal violation of the Bell inequalities are different from the nonequilibrium conditions which give the maximal entanglement. When the Bell inequality has asymmetric observables (between Alice and Bob), for example the I 3322 inequality, such asymmetry can also be reflected from the effects under the nonequilibrium environments. The spatial asymmetric two-qubit system coupled with nonequilibrium bosonic environments shows the thermal rectification effect, which can be witnessed by the Bell nonlocality. Different spatial asymmetric factors can be linearly cancelled with each other in the thermal rectification effect, which is also reflected on the changes of the entanglement and the Bell nonlocality. Our study demonstrates that the nonequilibrium environments are both valuable for the entanglement and Bell nonlocality resources, based on different optimal nonequilibrium conditions though. [ABSTRACT FROM AUTHOR]

The entangled qudits of three-level trapped ion and two phonons (in coherent state) in Λ configuration forming a Hilbert space of 12-D are investigated. The quantum entropy is analyzed "such as an elaborated measure" in trapped ion-coherent state system. Four values of Lamb-Dicke parameter (LDP), η = 0.005 , 0.07 , 0.08 and 0.09 are probed for deep Lamb-Dick regime. We elucidate that as η is increased, sudden death of entangled state in the trapped ion-coherent state system is decreased or vice versa. By this way, sudden birth of entangled state can be tuned by LDP. All graphs in this study are plotted with aid of the Wolfram Mathematica 9. [ABSTRACT FROM AUTHOR]

We investigate the entanglement of the ground state in the quantum cyclic graphs whose nodes are considered as quantum harmonic oscillators. To this end, the Schmidt numbers and entanglement entropy between two arbitrary partitions with equal nodes of a cyclic graphs, are calculated. For that, the local operation is used to build singular value decomposition of potential matrix of cyclic graphs. Then the maximum value of entanglement entropy among all bipartite cyclic graphs is obtained. [ABSTRACT FROM AUTHOR]

We analyse the entanglement of the light produced by a three-level laser whose cavity contains a parametric amplifier, with the cavity mode driven by the coherent light and coupled to a squeezed vacuum reservoir. Employing stochastic differential equations associated with the normal ordering resulted from the pertinent master equation, the quadrature variances and entanglement of the two-mode light are obtained and photon statistics of the two-light modes is discussed. It is found that the three-level laser generates squeezed light under certain conditions, with maximum intracavity squeezing being 89.7% below the coherent state level. We also show that the parametric amplifier enhances the mean photon number and photon number correlation. [ABSTRACT FROM AUTHOR]

We propose an optimal protocol for remotely preparing a four-qubit entangled state. In this protocol, a sender and two potential receivers share a ten-qubit entangled state. The sender performs a two-qubit state measurement based on the information of the quantum state that needs to be prepared. According to the measurement results of the sender, any potential receiver can obtain the quantum state that the sender needs to prepare by using the corresponding unitary transformation. [ABSTRACT FROM AUTHOR]

We propose a scheme of controlled teleportation of an arbitrary three-qubit state by using a five-qubit cluster state. In our scheme, the sender Alice performs five sets of single-qubit measurements and the controller Charlie needs only take a single-qubit measurement. The receiver Bob can reconstruct the arbitrary three-qubit state by performing the single-qubit unitary operations and a controlled-NOT operation if he obtains the help of the controller. We show that the efficiency in this scheme approaches 100% [ABSTRACT FROM AUTHOR]

Polarized light passing through twisted wave plates shows entangled state of both SAM and OAM. The polarization matrix and the polarized state are constructed on OAM sphere for l = 1 where m varies between l, 0, − l. The twisted birefringent matrix develops the twisted quarter- and half-wave plates which in turn identify various retarders. The variable circular and linear retarders (VCR and VLR) are studied here from the viewpoint of quantum processing of entangled states. Interestingly, the geometric phase in association with the gain of OAM has been studied here for the phase shifter of an antenna array. [ABSTRACT FROM AUTHOR]

In this paper, we study a model of two two-level atoms interacting with a quantum field. An analytical solution is obtained which is used to study the information entropy of the system. It is shown that the nonlinear term plays a significant role in the behaviour of the minimum uncertainty (MU) compared with the concurrence (C). Our extensive study of information entropy of atoms–field interaction demonstrates that using the coupling strength between the atoms and the field as a controller parameter, one can control the dynamics of the system by increasing the lower bound of the entropic uncertainty relation or decreasing the entanglement. [ABSTRACT FROM AUTHOR]

By repeated trials, one can determine the fairness of a classical coin with a confidence which grows with the number of trials. A quantum coin can be in a superposition of heads and tails and its state is most generally a density matrix. Given a string of qubits representing a series of trials, one can measure them individually and determine the state with a certain confidence. We show that there is an improved strategy which measures the qubits after entangling them, which leads to a greater confidence. This strategy is demonstrated on the simulation facility of IBM quantum computers. [ABSTRACT FROM AUTHOR]

In this paper, we put forward a scheme to realise joint remote state preparation (JRSP) of an arbitrary eight-qubit cluster-type state with two non-maximally entangled Greenberger–Horne–Zeilinger (GHZ) states in a recursive manner. The senders begin by helping the remote receiver to construct one intermediate state which is related to the target state closely. Then, the receiver introduces auxiliary qubits and applies appropriate local operations to obtain the target eight-qubit cluster-type state. It is shown that one new GHZ channel can be distributed among three participants with a certain probability if the initial attempt fails. Moreover, compared with the previous protocols, in our scheme both quantum resources and classical communications are considerably reduced. [ABSTRACT FROM AUTHOR]

Quantum privacy query (QPQ) is a cryptographic application that protects the privacy of both users and databases while querying the database secretly. In most existing QPQ protocols, the protection of user privacy can only be cheat-sensitive. Cheat-sensitive means that Bob will be found later with a certain probability if he tries to get the address queried by Alice. On the premise of cheat-sensitive, although Alice can discover Bob's malicious behavior after a query (transaction), the secret information of Alice was leaked in the completed query, which is likely to be a fatal blow to Alice. Or, to prevent Bob's malicious behavior, Alice executes one or more additional queries to test Bob's honesty. However, to bypass Alice's honesty test, Bob can also provide several honest queries before performing dishonest queries. Therefore, cheat-sensitive should not be the ultimate goal of user privacy protection in QPQ. In this paper, we propose a two-way QKD-based QPQ protocol with better user privacy protection than cheat-sensitive based on order rearrangement of qubits. The proposed QPQ protocol can resist the Trojan horse attack even without wavelength filter and photon number splitter equipped with auxiliary monitoring detectors. [ABSTRACT FROM AUTHOR]

We propose a scheme of controlled cyclic quantum teleportation of an arbitrary two-qubit entangled state by using a ten-qubit entangled state. In our scheme, Alice can teleport an arbitrary two-qubit entangled state to Bob, Bob can teleport an arbitrary two-qubit entangled state to Charlie and at the same time Charlie can teleport an arbitrary two-qubit entangled state to Alice with the help of the controller David. [ABSTRACT FROM AUTHOR]

We consider the case that the two-level atom off-resonantly interacts with cavity field via a one-photon hopping in double Jaynes-Cummings system. Geometrical quantum discord (GQD) is adopted to quantify the degree of correlation between two subsystems. GQD dynamics between two atoms, between cavity fields, as well as between atom and cavity fields are studied. The influences of detuning on GQD are discussed. The results obtained using the numerical method show that GQD between two atoms, between cavity fields, and between atom and cavity fields all display periodic oscillations. Furthermore, their periodic oscillations frequencies increase with the increase of detuning. On the other hand, GQD between two cavity fields and that between atom and cavity are weakened with increase of detuning. [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, the linear entropy and collapse-revival phenomenon through the relation (⟨a^+a^⟩-n¯) in a system of N-configuration four-level atom interacting with a single-mode field with additional forms of nonlinearities of both the field and the intensity-dependent atom-field coupling functional are investigated. A factorization of the initial density operator is assumed, considering the field to be initially in a squeezed coherent states and the atom initially in its most upper excited state. The dynamical behavior of the linear entropy and the time evolution of (⟨a^+a^⟩-n¯) are analyzed. In particular, the effects of the mean photon number, detuning, Kerr-like medium and the intensity-dependent coupling functional on the entropy and the evolution of (⟨a^+a^⟩-n¯) are examined. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the preservation of quantum Fisher information (QFI) of a single-qubit system coupled to a common zero temperature reservoir through the addition of noninteracting qubits. The results show that, the QFI is completely protected in both Markovian and non-Markovian regimes by increasing the number of additional qubits. Besides, the phenomena of QFI display monotonic decay or non-monotonic with revival oscillations depending on the number of additional qubits N − 1 in a common dissipative reservoir. If N < Nc (a critical number depending on the reservoirs parameters), the behavior of QFI with monotonic decay occurs. However, if N ≥ Nc, QFI exhibits non-monotonic behavior with revival oscillations. Moreover, we extend this model to investigate the effect of additional qubits and the initial conditions of the system on the geometric phase (GP). It is found that, the robustness of GP against the dissipative reservoir has been demonstrated by increasing gradually the number of additional qubits N − 1. Besides, the GP is sensitive to the initial parameter 휃, and possesses symmetric in a range regime [0,2π]. [ABSTRACT FROM AUTHOR]

We consider two independent models which consist of an ion interacting with laser field. The influence of the initial degree of entanglement of the two ions on the entanglement of internal states of ions, ion-ion vibration entanglement and ion vibration-ion vibration entanglement is discussed. We examine entanglement via concurrence and negativity, and find that the sum of entanglement between two ions and entanglement between two ion vibration states is conserved. It is shown that entanglement sudden death (ESD) can happen and the less the value of initial degree of entanglement of the two ions is, the longer the ESD time cost. The initial degree of entanglement of the two ions has no influence on the trends of the evolution of entanglement. The less value of the initial degree of entanglement of the two ions is, the smaller the peak value of the entanglement achieved. [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]

We investigate the dynamics of entanglement given by the concurrence of a two-qubit system in the non-Markovian setting. A quantum master equation is derived, which is solved in the eigenbasis of the system Hamiltonian for X-type initial states. A closed formula for time evolution of concurrence is presented for a pure state. It is shown that under the influence of dissipation non-zero entanglement is created in unentangled two-qubit states which decay in the same way as pure entangled states. We also show that under real circumstances, the decay rate of concurrence is strongly modified by the non-Markovianity of the evolution. [ABSTRACT FROM AUTHOR]

We present two schemes for transforming bipartite non-maximally entangled states into a W state in cavity QED system, by using highly detuned interactions and the resonant interactions between two-level atoms and a single-mode cavity field. A tri-atom W state can be generated by adjusting the interaction times between atoms and the cavity mode. These schemes demonstrate that two bipartite non-maximally entangled states can be merged into a maximally entangled W state. So the scheme can, in some sense, be regarded as an entanglement concentration process. The experimental feasibility of the schemes is also discussed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is a proposal on entanglement concentration protocol for cluster states. The protocol uses CNOT gate operation and is assisted with a single qubit. Moreover, the local and non-local operations are performed by a single party. We also make a comparative numerical study of the residual entanglement left out after the execution of each step of the protocol. [ABSTRACT FROM AUTHOR]

The idea of secure quantum information exchange (SQIE) [ J. Phys. B: At. Mol. Opt. Phys. 44, 115504 (2011)] is introduced for the secure exchange of single qubit information states between two legitimate users, Alice and Bob. In the present paper, we extend this original SQIE protocol by presenting a scheme, which enables the secure exchange of n-single qubit information states among the n nodes of a quantum network, with the aid of a special kind of 4 n-qubit entangled state and the classical assistance of an extra participant Charlie. For experimental realization of our extended SQIE protocol, we suggest an efficient scheme for the generation of a special kind of 4 n-qubit entangled state using the interaction between highly detuned Λ-type three-level atoms and optical coherent field. Further, by discussing the various experimental parameters, we show that the special kind 4 n-qubit entangled state can be generated with the presently available technology. [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 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]

Based on the Tavis-Cummings model, the entanglement dynamics between two atoms coupled nonsymmetrically to a single-mode $$l$$ -photon coherent field is investigated through analytical and numerical method. It is found that nonsymmetry plays a critical role in entangling two atoms and can lead to the sudden birth of entanglement, compared with a sudden death. Moreover, influences of coherent intensity, atom/field resonance order and squeezing order of coherent field upon entanglement evolution are also explored. [ABSTRACT FROM AUTHOR]

Based on resonant interactions between atoms and cavity modes, we have designed a scheme for expanding atomic entangled W states. By sending one of the atoms in a N-atom W state and an auxiliary excited-state atom into an vacuum cavity, we have obtained a ( N + 1)-atom W state by detecting the cavity field after interaction. The feasibility analysis indicates that this scheme may be implementable in near future. [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]

Fifty years ago Hartman studied the barrier transmission time of wave packets (J Appl Phys 33:3427-3433, ). He was inspired by the tunneling experiments across thin insulating layers at that time. For opaque barriers he calculated faster than light propagation and a transmission time independent of barrier length, which is called the Hartman effect. A faster than light (FTL or superluminal) wave packet velocity was deduced in analog tunneling experiments with microwaves and with infrared light thirty years later. Recently, the conjectured zero time of electron tunneling was claimed to have been observed in ionizing helium inside the barrier. The calculated and measured short tunneling time arises at the barrier front. This tunneling time was found to be universal for elastic fields as well as for electromagnetic fields. Remarkable is that the delay time is the same for the reflected and the transmitted waves in the case of symmetric barriers. Several theoretical physicists predicted this strange nature of the tunneling process. However, even with this background many members of the physics community do not accept a FTL signal velocity interpretation of the experimental tunneling results. Instead a luminal front velocity was calculated to explain the FTL experimental results frequently. However, Brillouin stated in his book on wave propagation and group velocity that the front velocity is given by the group velocity of wave packets in the case of physical signals, which have only finite frequency bandwidths. Some studies assumed barriers to be cavities and the observed tunneling time does represent the cavity lifetime. We are going to discus these continuing misleading interpretations, which are found in journals and in textbooks till today. [ABSTRACT FROM AUTHOR]

In this paper we have investigated the effect of temperature, magnetic field, and exchange coupling on the thermal entanglement in a spin chain with three particles in terms of the measure of entanglement called negativity. The results show that the entanglement decreases with increase in temperature. Also, we have found that under a uniform magnetic field in constant temperature, the entanglement decreases while passing through some maxima. We have found that increasing exchange coupling of any two particles decreases the entanglement of the other two particles. Finally, we have compared our system with a two-particle system and found that in presence of a magnetic field the increase in number of particles leads to the increase in the entanglement. [ABSTRACT FROM AUTHOR]