Search

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]

Within the framework of quantum information theory, the performance of conventional 2-D techniques is often unsatisfactory for the study of Bell states that hold a unique status as maximally entangled states. Therefore, 3-D approaches are increasingly employed to achieve more accurate and detailed analysis, offering improved performance and insights in complex scenarios. Among the diverse background of mixed two-qubit states, certain configurations exhibit unique quantum correlations that harness advanced quantum information processing tasks such as Bell diagonal states. Although, these states may appear superficially simple and exhibit a rich spectrum of correlations. The present research employs a methodology that involves a convex combination of distinct Bell states to generate the entire class of Bell diagonal states. This work explores the time evolution of Bell diagonal states, when exposed to various quantum channels and investigates the dynamics of quantum correlations such as entanglement, discord, and state of separability. Finally, the behaviour of Bell diagonal states is analysed and results are compared between theory and practice. A threedimensional visual approach is used to illustrate a deeper understanding of various quantum features and dynamic behaviour of the Bell diagonal states. [ABSTRACT FROM AUTHOR]

Using the powerful language of geometric algebra, we present an observationally symmetric derivation of the strong correlations predicted by the entangled singlet state in a deterministic and locally causal model, usually also referred to as a local-realistic model, in which the physical space is assumed to be a quaternionic 3-sphere, or S 3 , available as the spatial part of a solution of Einstein’s field equations of general relativity, and compare it in quantitative detail with Bell’s local-realistic model for the singlet correlations set within a flat Euclidean space I R 3 . Since the quantitatively detailed expressions of relative-angle-dependent probabilities of observing measurement outcomes for Bell’s local model do not seem to have been fully articulated before, our novel analysis exploiting the non-commutative properties of quaternions, in addition to allowing the comparison with the quaternionic 3-sphere model, may also provide useful comparisons for other less compelling local-realistic models, such as those relying on retrocausality or superdeterminism. Apart from the conservation of zero spin angular momentum, the key attribute underlying the strong singlet correlations within S 3 in comparison with Bell’s local model turns out to be the spinorial sign changes intrinsic to quaternions that constitute the 3-sphere. In addition, we also discuss anew a macroscopic experiment that can, in principle, test our 3-sphere hypothesis. [ABSTRACT FROM AUTHOR]

In this paper we describe remote state preparation schemes for a qubit through quantum walks on a line, a cycle and on a two-vertex complete graph. In all these three cases, there is no requirement for shared quantum entangled channels, which precludes the possibility of disturbances created by noisy environments. The state intended for remote preparation, although known to the intender, is not in the physical possession of any of the involved parties. The protocol proposed here is a perfect communication protocol. [ABSTRACT FROM AUTHOR]

The paper covers the analysis conducted to determine the effect, in terms of entanglement concurrence, of supplementing the tetrahedral spin s = 1 2 structure with additional central spin. The investigation is conducted with assumption that the system is coupled with the environment of Markovian nature. This work contains a comparison between three stuctures (unsupplemented, supplemented with spin s = 1 2 and supplemented with spin S = 1 ), with various exchange interaction parameters, taking into account also Dzyaloshinskii - Moriya (DM) and Kaplan - Shekhtman - Entin-Wohlman - Aharony (KSEA) interactions. The investigation reveals that by manipulating the anisotropy of the exchange interactions and DM coefficient, the effect of higher initial entanglement in supplemented structures can be obtained for particular initial states. [ABSTRACT FROM AUTHOR]

Current protocols face limitations due to the small number and single form of transmitted qubits, as well as the complexity involved in preparing quantum channels. To address these limitations and develop a novel and practical protocol, we propose a new symmetric cyclic controlled quantum teleportation protocol, using nineteen-qubit entangled state as the quantum channel. Specifically, Alice, Bob and Charlie cyclically send arbitrary three-qubit states among themselves with the help of the controller David. The specialty of the proposed protocol is the utilization of multiple easy-to-prepare Bell-states and single-qubits within the quantum channel, which effectively minimizes resource consumption. Furthermore, we generalize the protocol with n+1(n≥3) parties by using (6n+1)-qubit entangled state as the quantum channel. This paper briefly analyzes the security of the protocol and compares them with the previous protocols in terms of efficiency. The results show that the present protocol is secure and more efficient. Our scheme has the potential to play a crucial role in facilitating secure quantum communication between quantum nodes in quantum networks. [ABSTRACT FROM AUTHOR]

The four quantum noises-Bit Flip, Phase Flip, Depolarization, and Amplitude Damping-as well as any potential combinations of them, are examined in this paper’s investigation of quantum teleportation using qutrit states. Among the mentioned noises, we observed that phase flip has the highest fidelity. When compared to uncorrelated Amplitude Damping, we find that Correlated Amplitude Damping performs two times better. Finally, we conclude that for better fidelity, it is preferable to introduce the same noise in channel state if noise is unavoidable. [ABSTRACT FROM AUTHOR]

The fully entangled fraction (FEF) is related to many quantum information processes. In this paper, we propose a variational quantum algorithm to solve the FEF of a given quantum state without density matrix on near-term quantum devices without using quantum state tomography. By constructing parameterized circuit, we convert the problem that solving the FEF into the all-zero measurement probability of the final state. The FEF of Isotropic states and Werner states are simulated numerically and verified to be in agreement with the analytical solution. And the numerical experiments prove the feasibility of our algorithm. Our results can be used to detect entanglement or distillability without knowing the density matrix of quantum states. [ABSTRACT FROM AUTHOR]

This work presents a theoretical study on the behavior of global quantum discord and entanglement in two coupled double quantum dots made of AlGaAs/GaAs as a function of temperature. We use each double quantum dot as a qubit, where the electron can occupy either the right or left dot. The goal of our investigation is to understand the impact of the energy offset of each qubit and the tunneling coupling energy on quantum correlations. Our findings show that the energy offset and tunneling coupling energy significantly affect the variations of entanglement of formation, standard discord, and global quantum discord. Our results provide insights into the interplay between quantum correlations and environmental parameters and have important implications for the development of quantum technologies. [ABSTRACT FROM AUTHOR]

It is known that the adiabatic evolution and Berry phase of a quantum can be mapped into the classical dynamics and Hannay’s angle of coupled oscillators in a strictly mathematical way. In this work, we show that a quantum composite system consisting of two spin-1/2 can also be mapped into coupled two sets of classical oscillators by using this quantum-classical mapping. The evolution and geometric phase for the quantum composite system have been mapped into the classical dynamics and Hannay’s angle for the oscillators. The quantum entanglement has also been mapped into the correlation between the two sets of coupled oscillators. We also provide a way to study the classical geometric angle by mapping the geometric phases for the quantum subsystems into classical ones. Our results can provide a new way to simulate the quantum composite system and study the classical composite system. [ABSTRACT FROM AUTHOR]

We consider the dynamics of an ensemble of cold atoms coupled to light through radiation pressure in an optical lattice. We show that the steady-state displacement of the atomic ensemble shows bistable behavior which can be tuned by the position of the cold atoms in the Brillouin zone. Further, we describe a scheme to transfer the quantum state of the light field to the atomic field of two ensembles of cold atoms inside two independent optical cavities. This method leads to quantum entanglement which can be used in implementing quantum communication and computing. An Einstein-Podolsky-Rosen (EPR) state may be achieved with a judicious choice of parameters for our system. [ABSTRACT FROM AUTHOR]

We replace a Hamiltonian with a modular Hamiltonian in the spectral form factor and the level spacing distribution function. This study establishes a connection between quantities within Quantum Entanglement and Quantum Chaos. To have a universal study for Quantum Entanglement, we consider the Gaussian random 2-qubit model. The maximum violation of Bell’s inequality demonstrates a positive correlation with the entanglement entropy. Thus, the violation plays an equivalent role as Quantum Entanglement. We first provide an analytical estimation of the relation between quantum entanglement quantities and the dip when a subregion only has one qubit. The time of the first dip is monotone for entanglement entropy. The dynamics in a subregion is independent of the initial state at a late time. It is one of the signaling conditions for classical chaos. We also extend our analysis to the Gaussian random 3-qubit state, and it indicates a similar result. The simulation shows that the level spacing distribution function approaches GUE at a late time. In the end, we develop a technique within QFT to the spectral form factor for its relation to an n-sheet manifold. We apply the technology to a single interval in CFT2 and the spherical entangling surface in N = 4 super Yang-Mills theory. The result is one for both cases, but the Rényi entropy can depend on the Rényi index. For the case of CFT2, it indicates the difference between the continuum and discrete spectrum. [ABSTRACT FROM AUTHOR]

We consider how to generate entangled state of the coupled exciton-photon system in the semiconductor microcavities. Using short-time approximation, we calculate two different entanglement parameters. we show that entangled state can be generated in the dynamical processing. It shows that quantum entanglement decreases monotonically with the evolution and the stronger coupling constant of exciton-photon interaction induces better entanglement. [ABSTRACT FROM AUTHOR]

Possibility of using non-maximally entangled states in quantum bidirectional direct communication has been shown recently by Srikanth A and Balakrishnan (Quantum Inf. Process. 19:133, 2020) [1]. The effect of noise in this protocol is analyzed by considering amplitude and phase damping models. Suitable combinations of messages and initial states are identified to minimize the effect of noise in the protocol. Further, we have shown the possibility of demarking the effects due to noise and the intruder. [ABSTRACT FROM AUTHOR]

We investigate the entanglement behavior of two boson ensembles in weak population limit. We first obtain the analytical expressions of the wave function and the entanglement parameter. By numerically calculate entanglement parameter, we see that the better entanglement can be achieved by enhancing the nonlinearity, the coherent coupling and decreasing the interspecies interaction. [ABSTRACT FROM AUTHOR]

We study the influence of non-commutativity and the effects of the coupling constant between two modes harmonic oscillators interacting with its environment on quantum correlations. The considered system is two bilinearly coupled harmonic oscillators in non-commuting spatial coordinates coupled to its environment. The dynamics of the covariance matrix, the quantum discord for continuous variables Gaussian states in non-commutative space, the logarithmic negativity, and the quantum fidelity are used to evaluate the quantum correlations in the system, which is comparable to the commutative space case. We show that the quantum discord never disappears in a finite time in the both commutative and non-commutative space, thus containing all correlations (classical and quantum) in the system. In addition, we realize also that non-commutativity effects combined with the coupling constant lead to an increasing entanglement of the quantum states, and the quantum fidelity for continuous variables is shown not to be affected by the non-commutative deformation when single-mode Gaussian squeezed state is taken as an initial state. [ABSTRACT FROM AUTHOR]

As an analogy of the entangled fraction and coherence fraction, we have introduced the notion of quantum discord fraction, which quantifies the closeness between a given state and the set of maximally discord states. We also present a series of general properties of the quantum discord fraction: e.g., the boundedness, the asymmetry and the invariants under local-unitary transformations, which inherit from quantum discord. However, the similarity ends here: The quantum discord fraction in a bipartite quantum system can be convex. By providing a classification of quantum states in a bipartite quantum system, we have elucidated the relationship between the quantum discord fraction and the quantum entanglement fraction, especially the quantum discord fraction is always equal to the quantum entanglement fraction in any 2-qubit system. Moreover, the relationship between the quantum discord fraction and the relative entropy-based discord are also indicated. [ABSTRACT FROM AUTHOR]

We study the dynamics of entanglement and fidelity, in a one-dimensional spin-1/2 XX model with three-spin interaction (TSI) and Dzyaloshinski-Moriya interaction (DM). We select the nearest neighbor pair of spins as an open quantum system, and the rest of the chain is considered as the environment. Fidelity is compared with concurrence in systems with different interactions. The results show that the fidelity properly reflects the quantum entanglement of the spin chain. It is observed that increasing the exchange interaction parameter improves the consistency between fidelity and entanglement of the system. Moreover, the non- Markovian behavior of the system is studied. In the presence of three-spin interaction, the dynamics of the fidelity as well as entanglement strongly depends on the non-Markovian regime. In addition, in the non- Markovian regime, although fidelity exhibited better stability by passing the time, both the entanglement and fidelity reach to zero at the same time. This behavior has not been demonstrated in other research, so far. [ABSTRACT FROM AUTHOR]

We investigate the effect of Dzyaloshinskii-Moriya interaction and the anisotropy on the entanglement of the two-dimensional Heisenberg XXZ model. Concurrence and quantum Fisher information are computed to witness the entanglement. It is observed that the anisotropy suppresses the concurrence and this suppression can be compensated by the Dzyaloshinskii-Moriya interaction.We solved the model by using quantum renormalization group method and computed the unstable fixed points of the model and obtained the phase diagram of the model. In phase diagram, the critical line separates the two phases, the spinfluid phase and the N´eel phase. Interestingly, a variation in the quantum phase transition of the model is observed while tuning the Dzyaloshinskii-Moriya interaction. At phase transition point, the non analyticity using first derivative and the scaling behavior is studied for both, the concurrence and the quantum Fisher information. Moreover, the scaling exponent successfully describes the correlation length of the model at the critical point. [ABSTRACT FROM AUTHOR]

In this work we introduce a three-party quantum conference where the involved parties initially hold asymmetric quantum information which are finally shared amongst themselves by the execution of a quantum communication protocol. The three conferencing parties along with a controller are connected amongst themselves through a multipartite quantum entanglement which is used as quantum resource in the protocol. The role of the controller is confined to a final action without which the conference can not be performed. The present work is an instance of applications of multipartite entangled resources in communication problems. [ABSTRACT FROM AUTHOR]

Quantum coherence and quantum entanglement are two of the most important quantum properties, while the relationship between them hasn't been revealed completely, even though revealing their relationship is conducive to the development of quantum theory. In this work, we investigate their relationship in two-qubit pure states and Bell diagonal states, and we propose a relationship between coherence and entanglement. That is the sum of concurrence, l1 norm coherence of each subsystems and compensate factor equals to the intuitive l1 norm of coherence of the quantum system. Furthermore, we also investigate the relationship between Bell nonlocality and coherence. Then we check the correctness of our theories in some typical open systems by assuming one of the qubits passes through the noisy environment. The relationship we proposed here may deepen our understanding about quantum world. [ABSTRACT FROM AUTHOR]

We investigate the monogamy relations related to the concurrence, the entanglement of formation, convex-roof extended negativity, Tsallis-q entanglement and Rényi-α entanglement, the polygamy relations related to the entanglement of formation, Tsallis-q entanglement and Rényi-α entanglement. Monogamy and polygamy inequalities are obtained for arbitrary multipartite qubit systems, which are proved to be tighter than the existing ones. Detailed examples are presented. [ABSTRACT FROM AUTHOR]

Utilizing the advantage of quantum entanglement swapping, a multi-party quantum key agreement protocol with authentication is proposed. In this protocol, a semi-trusted third party is introduced, who prepares Bell states, and sends one particle to multiple participants respectively. After that the participants can share a Greenberger-Horne-Zeilinger state by entanglement swapping. Finally, these participants measure the particles in their hands and obtain an agreement key. Here, classical hash function and Hadamard operation are utilized to authenticate the identity of participants. The correlations of GHZ states ensure the security of the proposed protocol. To illustrated it detailly, the security of this protocol against common attacks is analyzed, which shows that the proposed protocol is secure in theory. [ABSTRACT FROM AUTHOR]

Currently, the creation of the quantum entanglement is still one of the most challenging goals. Here, we theoretically investigate the stationary entanglement between an optical cavity field mode and a cubic nonlinear vibrating mirror in an optomechanical system. We show that the mechanical nonlinearity gives rise to the enhancement of the maximum optomechanical entanglement, and shifts the maximum entanglement towards high effective cavity detuning values. We find that the mechanical nonlinearity makes the optomechanical entanglement more robust against the thermal noise of the surrounding environment. [ABSTRACT FROM AUTHOR]

The Majorana representation, which provides an intuitive way to represent the quantum state by stars on the Bloch sphere, has drawn considerable attention in the context of many body systems or systems with high-dimensional Hilbert space. In this work, we study Majorana representation for an interacting spin-1/2 composite system and its relation with the quantum correlation between the subsystems. Similar with the Majorana representation, we can define a new intuitive representation for the composite system by defining three stars which represents the dynamics and correlation of the two subsystems. The results show that, these two representations are the same for the separable case. The Berry phase has been found to be directly related to the concurrence between the two subsystems. By study the cases of no correlation and large correlation, the quantum entanglement and the Berry phases of the subsystem and their two representations on the Bloch sphere are discussed. These representations by stars provides a intuitive way to study the dynamics, entanglement and Berry phase composite system and its subsystems. [ABSTRACT FROM AUTHOR]

It has been known that quantum information offers powerful instruments to investigate the properties of many-body systems. In this framework, we touched two particular aspect of this activity, namely the quantum entanglement and discord to compare the properties of gapless Tomonaga-Luttinger Liquid (TLL) model and the effect of BCS coupling in spinless fermions of TLL as a cuprate superconducting nanowire. Using two-fermion space-spin density matrix, we investigate quantum correlation of these cases via bipartite and tripartite entanglement, as well as quantum discord. The relations of concurrence (as a measure of quantum entanglement), the lower bound of the generalized robustness of tripartite entanglement and quantum discord in terms of the relative distance between fermions and the coupling parameter were accordingly obtained. The relationship between the compressibility as a physical property of system and quantum correlations has also been studied. [ABSTRACT FROM AUTHOR]

We study unilateral coherence and coherence distribution in the background of a Schwarzschild black hole. We find that, comparing to the flat spacetime, two types of unilateral coherence corresponding to the measurements on system A and system B, respectively, are asymmetric for any Hawking temperature, and the accessible coherence of system B is bigger than the accessible coherence of system A in curved spacetime. We also find that the local coherence of system B reduces with the increase of Hawking temperature, while the local coherence of system A remains unchanged. Unlike behavior of quantum entanglement in curved spacetime, the remaining coherence (correlated coherence) increases with the increase of finitevalued Hawking temperature. [ABSTRACT FROM AUTHOR]

Quantum entanglement is one of the key methods in quantum information processing, but it is difficult to prepare quantum entanglement. Quantum walk is widely used in quantum computation and quantum simulation, it can be applied to the preparation of quantum entangled states. In this paper, a controllable quantum network coding scheme based on quantum walk is proposed. With the help of quantum walk, the scheme preliminary realized the entanglement distribution of butterfly network, reduced entanglement resources and enhanced scalability. According to the existing technology, it is feasible to implement the quantum network coding scheme proposed in this paper. [ABSTRACT FROM AUTHOR]

The dynamics of entanglement measured by concurrence and quantum correlation described by quantum discord under Ornstein-Uhlenbeck noise are investigated in several different cases. Our study mainly found that for both anti-ferromagnetic and ferromagnetic cases, the value of concurrence could be increased significantly by the cooperative effect of XZX+YZY and XZY-YZX three-site interactions. For anti-ferromagnetic case, XZY-YZX interaction has a positive effect on increasing the value of concurrence, nonetheless, for the ferromagnetic case, the XZX+YZY interaction plays a major role in enlarging and sustaining the value of concurrence. Whereas XZY-YZX interaction has a negative effect on concurrence for small J. The Non-Markovian case is much more effective than short-time limit or Markov limit case to preserve both concurrence and quantum discord. For small dissipation, the short-time limit is better than the Markov limit to prolong the lifetime of concurrence and quantum discord. For large dissipation, the Markov limit case is a preferable approximation. The entanglement sudden death time could be prolonged in the ferromagnetic case more than in the anti-ferromagnetic case. [ABSTRACT FROM AUTHOR]

The paper proposes a novel protocol of asymmetric cyclic controlled quantum teleportation, using a maximally nine-qubit entangled state as the quantum channel. In this protocol, communicants can simultaneously transmit two arbitrary two-qubit entangled states and an arbitrary single-qubit state. That is to say, Alice can transmit an arbitrary two-qubit state to Bob, Bob can transmit an arbitrary two-qubit state to Charlie, and Charlie can send an arbitrary single-qubit state to Alice via the control of David. Finally, the paper also analyzes and discusses the fidelity of the protocol in five different noise environments. [ABSTRACT FROM AUTHOR]

The protection of quantum entanglement has always been the focus of researchers. We adopt the scheme of combining weak measurement and measurement reversal to explore the protection effect of two-qutrit system in four noise channels, i.e., the amplitude damping channel, the phase damping channel, the bit flip channel and the depolarizing channel. For the given qutrits state with α = β = γ = 1 3 , it is found that the protection scheme can help to protect entanglement in the amplitude damping channel, while for the state with α = β = 1 2 , γ = 0 , the protection scheme plays a protective role in the amplitude damping channel and the depolarizing channel. We also calculate and discuss how the negativity and the probability of success behave when adjusting the weak measurement or measurement reversal strength. In different noise channels, the entanglement can be kept as much as possible by choosing the appropriate weak measurement parameters. It provides a strong basis for the system to maintain maximum entanglement in different noise channels. [ABSTRACT FROM AUTHOR]

We study the Bell nonlocality of high dimensional quantum systems based on quantum entanglement. A quantitative relationship between the maximal expectation value B of Bell operators and the quantum entanglement concurrence C is obtained for even dimension pure states, with the upper and lower bounds of B governed by C. [ABSTRACT FROM AUTHOR]

Quantum teleportation provides a way to transmit information from one location to another via a quantum channel. In traditional teleportation schemes, if the quantum channel is a non-maximally entangled quantum state, the success probability of teleporting an unknown three-dimensional quantum state can not be reached 100%. Here we propose a deterministic teleportation scheme to overcome this challenge, and our results show that the success probability of teleporting a three-dimensional quantum state can be increased to 100%. In particular, we have analyzed the security of our teleportation process, including particle transmission, and proved this process safe. Our scheme has high experimental feasibility. [ABSTRACT FROM AUTHOR]

A two-party quantum private comparison (QPC) protocol is constructed with four-particle entangled states, where the third party (TP) is assumed to be semi-honest in the sense that she is allowed to misbehave on her own but cannot conspire with anyone else. The proposed protocol is secure against both the outside attack and the participant attack, and only needs single-particle measurements, neither unitary operations nor quantum entanglement swapping. Without considering the security check process, the qubit efficiency of the proposed protocol attains as high as 25%. [ABSTRACT FROM AUTHOR]

A teleportation protocol for certain class of ten-qubit state by utilizing an eight-qubit entangled state as a quantum channel has been proposed. In this paper, we present an optimal scheme for the teleportation of a ten-qubit state by using a stochastic local operation and classical communication(SLOCC) equivalent to four-qubit χ state as entanglement channel. Only von Neumann type measurement, controlled-not (CNOT) operations and appropriate unitary operations are needed in this scheme. Receiver Bob can reconstruct the initial state by introducing the appropriate unitary transformation and auxiliary particles. [ABSTRACT FROM AUTHOR]

There are some interesting properties in quantum mechanics, such as quantum superposition and entanglement. We can use these features to solve some specific problems. Quantum computer has more advantages than classical computer in many problems. In this paper, we are interested in regular graph. A special case of graph structure destroyed is given. We present a search algorithm to find exceptional vertexes in the graph in this case. The algorithm uses the trick of amplitude amplification in quantum search algorithm. In the corresponding classical algorithm, the adjacency matrix may be used to store the information of vertex and edge of graph. It takes one time for the best and N times for the worst to find the target. Which means that N/2 times on average need to be conducted. In our quantum algorithm, nodes and vertexes are stored in quantum states, using quantum search to design algorithm. The search process can be accelerated in our quantum algorithm. [ABSTRACT FROM AUTHOR]

Importance of quantum entanglement has been demonstrated in various applications. Usually, separability of a bipartite state is defined by its algebraic structure, i.e. a convex combination of product states. But it seems to be hard to check separability (equivalently, entanglement) of a state from its algebraic structure. In this note, we give some characterizations of separability of bipartite states based on POVM measurements. For bipartite pure states, we prove the separability, Bell locality, unsteerability and classical correlation are the same. As a consequence, every entangled pure bipartite state is always Bell nonlocal, steerable and quantum correlated. [ABSTRACT FROM AUTHOR]

In this paper, a controlled multi-hop quantum teleportation of arbitrary single qubit state is given. Quantum information can be transmitted hop by hop perfectly under some controllers' helps. The partially entangled state used as quantum channel in the scheme can be produced from a partially GHZ state. Furthermore, only unitary operation, measurement with Bell state and classical base are needed in the scheme. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the entanglement of a quantum system containing two subsystems characterized by the angular momenta j1 and j2, in the framework of the superposition of spin coherent states. We formulate the measure of the entanglement in terms of the amplitudes of the spin coherent states as well as their spins j1 and j2. We extend this investigation to rank-two bipartite mixed states involving spin-j coherent states by using a simplified expression of concurrence. We show that the bipartite entanglement of mixed states is strongly dependent on the spin ji of each subsystem and the probabilities associated with it. [ABSTRACT FROM AUTHOR]

The exploration of quantum entanglement in multipartite quantum systems is of great significance to the study of quantum entanglement, maximally multi-qubit entangled state is one of the research objects. Recently, Che et al. presented a recurrence relation of multi-qubit state. According to this inspiration, we present the recurrence relation of maximally multi-qubit pure states of N-qubits for N = 6, 7, 8. Further, some new forms of the seven- and eight-qubit maximally entangled states are found with the recurrence relation. [ABSTRACT FROM AUTHOR]

We propose a scheme to investigate the behavior of a ballistic nanowire system with Rashba interaction within a perpendicular magnetic field. The quantum entanglement of a nanowire system is discussed via the negativity. When the strong and weak magnetic fields are applied, we discuss the influence of the spin-orbit interaction and the initial states on the population inversion and the negativity. Our results show that the degree of entanglement for the nanowire system mainly depends on the effect of the spin-orbit interaction and the initial states of the system. This opens up new avenues for designing nanowire systems for future quantum computation and communication applications. [ABSTRACT FROM AUTHOR]

We present a novel scheme of cyclic remote state preparation via a six-qubit entangled state as the quantum channel. By introducing three auxiliary particles and using feedforward measurement strategy, Alice can remotely prepare an arbitrary single-qubit quantum state for Bob, Bob can remotely prepare an arbitrary single-qubit quantum state on Charlie's site and Charlie can also remotely prepare an arbitrary single-qubit quantum state for Alice. It is pointed out that the cyclic remote preparation in the opposite direction can be perfectly achieved by changing the quantum channel. Furthermore, we generalize the above scheme to systems having N observers, so that cyclic remote state preparation can be realized in quantum information networks with N observers in different directions by changing quantum channels. [ABSTRACT FROM AUTHOR]

We investigate the notion of uncertainty region using the variance based sum uncertainty relation for qubits and qutrits. We compare uncertainty region of the qubit (a 2-level system) with that of the qutrit (3-level system) by considering sum uncertainty relation for two non-commuting Pauli-like observables, acting on the two dimensional qubit Hilbert space. We identify that physically valid uncertainty region of a qubit is smaller than that of a qutrit. This implies that an enhanced precision can be achieved in the measurement of incompatible Pauli-like observables acting on the 2-dimensional subspace of a qutrit Hilbert space. We discuss the implication of the reduced uncertainties in the steady states of Λ, V, Ξ types of 3-level atomic systems. Furthermore, we construct a two-qubit permutation symmetric state, corresponding to a 3-level system and show that the reduction in the sum uncertainty value - or equivalently, increased uncertainty region of a qutrit system – is a consequence of quantum entanglement in the two-qubit system. Our results suggest that uncertainty region can be used as a dimensional witness. [ABSTRACT FROM AUTHOR]

Recently, Zhang et al. raised two classes of orthogonal product states which cannot be exactly discriminated by local operations and classical communication (LOCC) in the quantum system of (2k + 1) ⊗ 2l and (3k + i) ⊗ (3l + j) (Sci. Rep. 6, 28864, 2016). However, it remains a meaningful question that what entanglement resources are necessary and/or sufficient for this task to be possible with LOCC. In this paper, we present a method of using only an auxiliary 2 ⊗ 2 maximally entangled state to complete the local discrimination. Specifically, by utilizing a two-qubit maximally entangled state as an ancillary resource, we propose a concrete protocol respectively to locally identify orthogonal product states in 5 ⊗ 6 and 5 ⊗ 5. Then we generalize the distinguishing method respectively to the states in the quantum system of (2k + 1) ⊗ 2l and (3k + i) ⊗ (3l + j). These results can make us have a better understanding of the relationship between quantum entanglement and quantum nonlocality. [ABSTRACT FROM AUTHOR]

In this work, we give an analytical derivation of the reduced density matrix between two qubits in a cavity field, which is described by the quantum Rabi model. Using the coherent state method and the generalized hypergeometric functions, we find a complete solution of the 4-by-4 reduced density matrix for each eigen energy by taking the partial trace over the cavity field states. Four kinds of measurements used to describe the quantum entanglement and quantum correlation between the two qubits, i.e., the concurrence, quantum discord, steerable weight, and robustness of coherence, are calculated for the ground state and excited states. For both the weak coupling (g → 0 ) and deep-strong coupling (g → ∞ ) regimes, quantum entanglement and quantum correlation between the two qubits are vanishing. An appropriate coupling in the deep strong coupling regime between the qubits and the cavity field is required if one wants to establish quantum entanglement between the qubits. [ABSTRACT FROM AUTHOR]

BB84-state is the non-orthogonal single-photon state which has the advantage of easy implementation compared with the quantum multi-photon entanglement states. In this paper, based on BB84-state, by introducing a trusted third-party voting center, a quantum voting scheme is proposed. In this scheme, by performing corresponding unitary operation on BB84-state, all voters send their voting information to the tallyman Charlie, then Charlie counts all votes under the supervision of voting management center Bob, which ensures that the protocol can resist inside attacks. Moreover, by utilizing the decoy particles, our scheme can efficiently prevent outside attacks. Compared with other related quantum voting protocols, our protocol has higher qubit efficiency and fewer interactive times. [ABSTRACT FROM AUTHOR]

A novel practical quantum secure direct communication (QSDC) protocol is constructed by utilizing the evolution law of atom via cavity QED. It transmits the atoms from one communicant to the other communicant in a two-step manner. It adopts two-atom product states as the initial quantum resource and the decoy atom technique to guarantee the security against the outside attack. It only needs single-atom measurements, and neither the quantum entanglement swapping nor the unitary operations. [ABSTRACT FROM AUTHOR]

We study the thermal entanglement of Heisenberg XXX model in an external magnetic field by using the method of concurrence. We study the quantum entanglement in the two qubit XXX model and XXZ model, and apply independent controllable external magnetic field to the two qubits respectively, and discuss the behavior of quantum entanglement by changing the coupling parameters, magnetic field and magnetic field. The results show that the behavior of quantum entanglement is different in a certain range of parameters. [ABSTRACT FROM AUTHOR]

We investigate the dynamical behaviors of quantum-memory-assisted entropic uncertainty relation (QMA-EUR) and quantum correlation (both quantum entanglement and quantum discord) for a two-qubit system coupled to a spin environment by a z–x-type interaction. Our purpose is to find out how the QMA-EUR and quantum correlations are affected by the pre-designed factors of the environment, including initial spin environmental states and the coupling constants. The numerical results show that the initial environmental state has significant effect on the dynamics of quantum correlations of the central spin system. We find that the environment should be prepared in a block entangled state with Bell state. This option is beneficial to reducing entropic uncertainty and inhibits the damping of quantum correlation. We also find that the high frequency particles in a spin bath can significantly enhance the robustness of quantum correlation of the system. [ABSTRACT FROM AUTHOR]

We work out a quantum-theoretic model in complex Hilbert space of a recently performed test on co-occurrencies of two concepts and their combination in retrieval processes on specific corpuses of documents. The test violated the Clauser-Horne-Shimony-Holt version of Bell's inequalities ('CHSH inequality'), thus indicating the presence of entanglement between the combined concepts. We make use of a recently elaborated 'entanglement scheme' and represent the collected data in the tensor product of Hilbert spaces of the individual concepts, showing that the identified violation is due to the presence of a strong form of entanglement, involving both states and measurements and reflecting the meaning connection between the component concepts. These results provide a significant confirmation of the presence of quantum structures in corpuses of documents, like it is the case for the entanglement identified in human cognition. [ABSTRACT FROM AUTHOR]