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      Thermal robustness of multipartite entanglement of the 1-D spin 1/2 XY model

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          Abstract

          We study the robustness of multipartite entanglement of the ground state of the one-dimensional spin 1/2 XY model with a transverse magnetic field in the presence of thermal excitations, by investigating a threshold temperature, below which the thermal state is guaranteed to be entangled. We obtain the threshold temperature based on the geometric measure of entanglement of the ground state. The threshold temperature reflects three characteristic lines in the phase diagram of the correlation function. Our approach reveals a region where multipartite entanglement at zero temperature is high but is thermally fragile, and another region where multipartite entanglement at zero temperature is low but is thermally robust.

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          Entanglement of Formation of an Arbitrary State of Two Qubits

          The entanglement of a pure state of a pair of quantum systems is defined as the entropy of either member of the pair. The entanglement of formation of a mixed state is defined as the minimum average entanglement of an ensemble of pure states that represents the given mixed state. An earlier paper [Phys. Rev. Lett. 78, 5022 (1997)] conjectured an explicit formula for the entanglement of formation of a pair of binary quantum objects (qubits) as a function of their density matrix, and proved the formula to be true for a special class of mixed states. The present paper extends the proof to arbitrary states of this system and shows how to construct entanglement-minimizing pure-state decompositions.
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            Persistent entanglement in arrays of interacting particles

            We study the entanglement properties of a class of \(N\) qubit quantum states that are generated in arrays of qubits with an Ising-type interaction. These states contain a large amount of entanglement as given by their Schmidt measure. They have also a high {\em persistency of entanglement} which means that \(\sim N/2\) qubits have to be measured to disentangle the state. These states can be regarded as an entanglement resource since one can generate a family of other multi-particle entangled states such as the generalized GHZ states of \(
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              Robustness of entanglement

              In the quest of completely describing entanglement in the general case of a finite number of parties sharing a physical system of finite dimensional Hilbert space a new entanglement magnitude is introduced for its pure and mixed states: robustness. It corresponds to the minimal amount of mixing with locally prepared states which washes out all entanglement. It quantifies in a sense the endurence of entanglement against noise and jamming. Its properties are studied comprehensively. Analytical expressions for the robustness are given for pure states of binary systems, and analytical bounds for mixed states of binary systems. Specific results are obtained mainly for the qubit-qubit system. As byproducts local pseudomixtures are generalized, a lower bound for the relative volume of separable states is deduced and arguments for considering convexity a necessary condition of any entanglement magnitude are put forward.

                Author and article information

                Journal
                23 June 2008
                2009-03-11
                Article
                10.1103/PhysRevA.79.042313
                0806.3644
                721f4833-2f1f-4004-92f4-74b4ff390cff

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Custom metadata
                Phys. Rev. A 79, 042313 (2009)
                Revised, 11 pages, 7 figures
                quant-ph

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