We point out that a geometric measure of quantum entanglement is related to the matrix permanent when restricted to permutation invariant states. This connection allows us to interpret the permanent as an angle between vectors. By employing a recently introduced permanent inequality [Carlen, Loss and Lieb, Meth. and Appl. of Analysis, 13 (2006), no. 1, 1–17], we can write combinatorial formulas for quantifying the entanglement of permutation invariant basis states. When applying the geometric measure to permutation invariant states with nonnegative coefficients, we show that the overlap with a product state is maximized by a tensor product of the same single-party state. This extends some observations in [Hayashi et al., Phys. Rev. A 77, 012104 (2008)].We point out that a geometric measure of quantum entanglement is related to the matrix permanent when restricted to permutation invariant states. This connection allows us to interpret the permanent as an angle between vectors. By employing a recently introduced permanent inequality [Carlen, Loss and Lieb, Meth. and Appl. of Analysis, 13 (2006), no. 1, 1–17], we can write combinatorial formulas for quantifying the entanglement of permutation invariant basis states. When applying the geometric measure to permutation invariant states with nonnegative coefficients, we show that the overlap with a product state is maximized by a tensor product of the same single-party state. This extends some observations in [Hayashi et al., Phys. Rev. A 77, 012104 (2008)].

Jan 1, 200945 citations

Generalized Matrix Functions and Geometric Measure of Entanglement

Vehbi Emrah Paksoy, Fuzhen Zhang, Haixia Chang

Given a complex n × n matrix A and an irreducible character χ of permutation group on n letters, generalized matrix function dχ(A) of A can be thought as combinatorial generalization of matrix permanent and determinant. Due to its combinatorial nature, it is usually a demanding task to assign the construction some geometrical meaning. In this presentation, we discuss how generalized matrix functions serve as essential tools in determining geometric measure of entanglement of certain quantum states. Along the way, we obtain some unexpected geometric interpretations and investigate some examples.Given a complex n × n matrix A and an irreducible character χ of permutation group on n letters, generalized matrix function dχ(A) of A can be thought as combinatorial generalization of matrix permanent and determinant. Due to its combinatorial nature, it is usually a demanding task to assign the construction some geometrical meaning. In this presentation, we discuss how generalized matrix functions serve as essential tools in determining geometric measure of entanglement of certain quantum states. Along the way, we obtain some unexpected geometric interpretations and investigate some examples.

Jan 1, 20160 citations

Connections of geometric measure of entanglement of pure symmetric states to quantum state estimation

Lin Chen, Huangjun Zhu, Tzu-Chieh Wei

We study the geometric measure of entanglement (GM) of pure symmetric states related to rank 1 positive-operator-valued measures (POVMs) and establish a general connection with quantum state estimation theory, especially the maximum likelihood principle. Based on this connection, we provide a method for computing the GM of these states and demonstrate its additivity property under certain conditions. In particular, we prove the additivity of the GM of pure symmetric multiqubit states whose Majorana points under Majorana representation are distributed within a half sphere, including all pure symmetric three-qubit states. We then introduce a family of symmetric states that are generated from mutually unbiased bases and derive an analytical formula for their GM. These states include Dicke states as special cases, which have already been realized in experiments. We also derive the GM of symmetric states generated from symmetric informationally complete POVMs (SIC POVMs) and use it to characterize all inequivalent SIC POVMs in three-dimensional Hilbert space that are covariant with respect to the Heisenberg-Weyl group. Finally, we describe an experimental scheme for creating the symmetric multiqubit states studied in this article and a possible scheme for measuring the permanence of the related Gram matrix.We study the geometric measure of entanglement (GM) of pure symmetric states related to rank 1 positive-operator-valued measures (POVMs) and establish a general connection with quantum state estimation theory, especially the maximum likelihood principle. Based on this connection, we provide a method for computing the GM of these states and demonstrate its additivity property under certain conditions. In particular, we prove the additivity of the GM of pure symmetric multiqubit states whose Majorana points under Majorana representation are distributed within a half sphere, including all pure symmetric three-qubit states. We then introduce a family of symmetric states that are generated from mutually unbiased bases and derive an analytical formula for their GM. These states include Dicke states as special cases, which have already been realized in experiments. We also derive the GM of symmetric states generated from symmetric informationally complete POVMs (SIC POVMs) and use it to characterize all inequivalent SIC POVMs in three-dimensional Hilbert space that are covariant with respect to the Heisenberg-Weyl group. Finally, we describe an experimental scheme for creating the symmetric multiqubit states studied in this article and a possible scheme for measuring the permanence of the related Gram matrix.

arXiv:1010.2361Physical Review AJan 13, 201117 citations

Entanglement and symmetry in permutation-symmetric states

Damian Markham

We investigate the relationship between multipartite entanglement and symmetry, focusing on permutation symmetric states. We give a highly intuitive geometric interpretation to entanglement via the Majorana representation, where these states correspond to points on a unit sphere. We use this to show how various entanglement properties are determined by the symmetry properties of the states. The geometric measure of entanglement is thus phrased entirely as a geometric optimization and a condition for the equivalence of entanglement measures written in terms of point symmetries. Finally, we see that different symmetries of the states correspond to different types of entanglement with respect to interconvertibility under stochastic local operations and classical communication.We investigate the relationship between multipartite entanglement and symmetry, focusing on permutation symmetric states. We give a highly intuitive geometric interpretation to entanglement via the Majorana representation, where these states correspond to points on a unit sphere. We use this to show how various entanglement properties are determined by the symmetry properties of the states. The geometric measure of entanglement is thus phrased entirely as a geometric optimization and a condition for the equivalence of entanglement measures written in terms of point symmetries. Finally, we see that different symmetries of the states correspond to different types of entanglement with respect to interconvertibility under stochastic local operations and classical communication.

arXiv:1001.0343Physical Review AApr 25, 201187 citations

Geometric measure of entanglement and applications to bipartite and multipartite quantum states

Tzu-Chieh Wei, Paul M. Goldbart

The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement, already present in a number of settings [A. Shimony, Ann. NY. Acad. Sci. 755, 675 (1995); H. Barnum and N. Linden, J. Phys. A: Math. Gen. 34, 6787 (2001)], is explored for bipartite and multipartite pure and mixed states. The measure is determined analytically for arbitrary two-qubit mixed states and for generalized Werner and isotropic states, and is also applied to certain multipartite mixed states. In particular, a detailed analysis is given for arbitrary mixtures of three-qubit Greenberger-Horne-Zeilinger, W, and inverted- $W$ states. Along the way, we point out connections of the geometric measure of entanglement with entanglement witnesses and with the Hartree approximation method.The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement, already present in a number of settings [A. Shimony, Ann. NY. Acad. Sci. 755, 675 (1995); H. Barnum and N. Linden, J. Phys. A: Math. Gen. 34, 6787 (2001)], is explored for bipartite and multipartite pure and mixed states. The measure is determined analytically for arbitrary two-qubit mixed states and for generalized Werner and isotropic states, and is also applied to certain multipartite mixed states. In particular, a detailed analysis is given for arbitrary mixtures of three-qubit Greenberger-Horne-Zeilinger, W, and inverted-$W$ states. Along the way, we point out connections of the geometric measure of entanglement with entanglement witnesses and with the Hartree approximation method.

arXiv:quant-ph/0307219Physical Review AOct 9, 2003744 citations

Quantum entanglement: geometric quantification and applications to multi-partite states and quantum phase transitions

Tzu-Chieh Wei

The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement is explored for bi-partite and multi-partite pure and mixed states. It is determined analytically for arbitrary two-qubit mixed states, generalized Werner, and isotropic states, and is also applied to certain multi-partite mixed states, including two distinct multi-partite bound entangled states. Moreover, the ground-state entanglement of the XY model in a transverse field is calculated and shown to exhibit singular behavior near the quantum critical line. Along the way, connections are pointed out between the geometric measure of entanglement, the Hartree approximation, entanglement witnesses, correlation functions, and the relative entropy of entanglement.The degree to which a pure quantum state is entangled can be characterized by the distance or angle to the nearest unentangled state. This geometric measure of entanglement is explored for bi-partite and multi-partite pure and mixed states. It is determined analytically for arbitrary two-qubit mixed states, generalized Werner, and isotropic states, and is also applied to certain multi-partite mixed states, including two distinct multi-partite bound entangled states. Moreover, the ground-state entanglement of the XY model in a transverse field is calculated and shown to exhibit singular behavior near the quantum critical line. Along the way, connections are pointed out between the geometric measure of entanglement, the Hartree approximation, entanglement witnesses, correlation functions, and the relative entropy of entanglement.

arXiv:0905.2467May 15, 20090 citations

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states. Along the way, we point out connections of the geometric measure of entanglement with entanglement witnesses and with the Hartree approximation method.