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The influence of white and color noise on the outcome of the entanglement swapping process is investigated in a four-qu bit system. Critical degree of noise in initial state, that could destroy entanglement in a result state is pr...
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The influence of white and color noise on the outcome of the entanglement swapping process is investigated in a four-qu bit system. Critical degree of noise in initial state, that could destroy entanglement in a result state is presented. The entanglement characteristics, such as concurrence, tangle, etc. are compared. Results could be helpful for experiments regarding entanglement swapping as conditions for initial quantum entangled states, to obtain entangled result state.
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In this paper, we propose a multipartite entanglement measure for arbitrary pure states, which is presented based on reduced density matrices of multi-qudit pure states. We review some multipartite entanglement measures based on d...
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In this paper, we propose a multipartite entanglement measure for arbitrary pure states, which is presented based on reduced density matrices of multi-qudit pure states. We review some multipartite entanglement measures based on density matrices. This is helpful for us to introduce a new good entanglement measure, which is vanishing if and only if a state is separable, invariant under local unitary transformations and non-increasing under local operations assisted by classical communication. We apply our entanglement measure for some explicit examples. It demonstrates that our entanglement measure is practical and convenient for computation. It can also distinguish the relatively high entanglement and the maximal entanglement. In short, our entanglement measure is good at characterizing multipartite entanglement.
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In this paper, we present a new approach to study genuine tripartite entanglement existing in (2 x 2 x n)-dimensional quantum pure states. By utilizing the approach, we introduce a particular quantity to measure genuine tripartite...
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In this paper, we present a new approach to study genuine tripartite entanglement existing in (2 x 2 x n)-dimensional quantum pure states. By utilizing the approach, we introduce a particular quantity to measure genuine tripartite entanglement. The quantity is shown to be an entanglement monotone in 2-dimensional subsystems (semi-monotone) and reaches zero for separable states and (2 x 2 x 2)-dimensional W states, hence is a good criterion to characterize genuine tripartite entanglement. Furthermore, the formulation for pure states can be conveniently extended to the case of mixed states by utilizing the kronecker product approximation technique. As applications, we give the analytic approximation for weakly mixed states, and study the genuine tripartite entanglement of two given weakly mixed states.
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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...
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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.
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Consider three qubits A, B, and C which may be entangled with each other. We show that there is a trade-off between A's entanglement with B and its entanglement with C. This relation is expressed in terms of a measure of entanglem...
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Consider three qubits A, B, and C which may be entangled with each other. We show that there is a trade-off between A's entanglement with B and its entanglement with C. This relation is expressed in terms of a measure of entanglement called the concurrence, which is related to the entanglement of formation. Specifically, we show that the squared concurrence between A and B, plus the squared concurrence between A and C, cannot be greater than the squared concurrence between A and the pair BC. This inequality is as strong as it could be, in the sense that for any values of the concurrences satisfying the corresponding equality, one can find a quantum state consistent with those values. Further exploration of this result leads to a definition of an essential three-way entanglement of the system, which is invariant under permutations of the qubits. [References: 26]
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Nonlocal unitary operations can create quantum entanglement between distributed particles, and the quantification of created entanglement is a hard problem. It corresponds to the concepts of entangling and assisted entangling powe...
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Nonlocal unitary operations can create quantum entanglement between distributed particles, and the quantification of created entanglement is a hard problem. It corresponds to the concepts of entangling and assisted entangling power when the input states are, respectively, product and arbitrary pure states.We analytically derive them for Schmidt-rank-two bipartite unitary and some complex bipartite permutation unitaries. In particular, the entangling power of permutation unitary of Schmidt rank three can take only one of two values: log_2 9 ? 16/9 or log_2 3 ebits. The entangling power, assisted entangling power, and disentangling power of 2 × d_B permutation unitaries of Schmidt rank four are all 2 ebits. These quantities are also derived for generalized Clifford operators. We further show that any bipartite permutation unitary of Schmidt rank greater than two has entangling power greater than 1.223 ebits. We construct the generalized controlled-NOT (CNOT) gates whose assisted entangling power reaches the maximum.We quantitatively compare the entangling power and assisted entangling power for general bipartite unitaries and their connection to the disentangling power by proposing a probabilistic protocol for implementing bipartite unitaries.
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We introduce a simple algebraic approach to the study of multipartite entanglement for pure states together with a class of suitable functionals able to detect the entanglement. On this basis, we reproduce some known results. Inde...
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We introduce a simple algebraic approach to the study of multipartite entanglement for pure states together with a class of suitable functionals able to detect the entanglement. On this basis, we reproduce some known results. Indeed, by investigating the properties of the introduced functionals, we show that a subset of such class is strictly connected to the purity. Moreover, we provide a direct and basic solution to the problem of simultaneous maximization of three appropriate functionals for three-qubit states, confirming that the simultaneous maximization of the entanglement for all possible bipartitions is compatible only with the structure of the GHZ states.
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We consider entanglement entropy in the context of gauge/gravity duality for conformal field theories in even dimensions. The holographic prescription due to Ryu and Takayanagi (RT) leads to an equation describing how the entangli...
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We consider entanglement entropy in the context of gauge/gravity duality for conformal field theories in even dimensions. The holographic prescription due to Ryu and Takayanagi (RT) leads to an equation describing how the entangling surface extends into the bulk geometry. We show that setting to zero, the time-time component of the Brown-York stress tensor evaluated on the co-dimension 1 entangling surface, leads to the same equation. By considering a spherical entangling surface as an example, we observe that the Euclidean action methods in AdS/CFT will lead to the RT area functional arising as a counterterm needed to regularize the stress tensor. We present arguments leading to a justification for the minimal area prescription.
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Using a rigorous quantum model a comprehensive study of physical properties of entangled photon pairs generated in spontaneous parametric downconversion in chirped periodically poled crystals is presented. Spec-tral, temporal, as ...
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Using a rigorous quantum model a comprehensive study of physical properties of entangled photon pairs generated in spontaneous parametric downconversion in chirped periodically poled crystals is presented. Spec-tral, temporal, as well as spatial characteristics of photon pairs are analyzed. Spectral bandwidths, photon-pair flux, and entanglement area can be effectively controlled by chirping. Quantification of entanglement between photons in a pair is given. Splitting of entanglement area in the transverse plane accompanied by spectral splitting has been revealed. Using the model temperature dependencies of the experimental intensity profiles reported in literature have been explained.
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We develop an approach of quantifying entanglement in mixed quantum states by the optimal entanglement witness operator. We identify the convex set of mixed states for which a single witness provides the exact value of an entangle...
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We develop an approach of quantifying entanglement in mixed quantum states by the optimal entanglement witness operator. We identify the convex set of mixed states for which a single witness provides the exact value of an entanglement measure and show that the convexity, properties, and symmetries of entanglement or of a target state considerably fix the form of the optimal witness. This greatly reduces the difficulty in computing and experimentally determining entanglement measures. As an example, we show how to experimentally quantify bound entanglement in four-qubit noisy Smolin states and three-qubit Greenberger-Horne-Zeilinger entanglement under white noise. For general measures and states, we provide a numerical method to efficiently optimize the witness.
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