It is a recent observation that entanglement classification for qubits is closely related to local SL(2,C)-invariants including the invariance under qubit permutations [Dür, et al., Phys. Rev. A 62, 062314 (2000); Osterloh, A. and Siewert, J., Phys. Rev. A 72, 012337 (2005); O. Chterental and D. Ž. Ðoković, Linear Algebra Research Advances (Nova Science, Hauppauge, N.Y., 2007), Chap. 4, p. 133], which has been termed SL∗ invariance. In order to single out the SL∗ invariants, we analyze the SL(2,C)-invariants of four (five) qubits and decompose them into irreducible modules for the symmetric group S4 (S5) of qubit permutations. A classifying set of measures of genuine multipartite entanglement is given by the ideal of the algebra of SL∗-invariants vanishing on arbitrary product states. We find that low degree homogeneous components of this ideal can be constructed in full by using the approach introduced by Osterloh and Siewert [Phys. Rev. A 72, 012337 (2005); Int. J. Quant. Inf. 4, 531 (2006)]. Our analysis highlights an intimate connection between this latter procedure and the standard methods to create invariants, such as the Ω-process [Luque, J.-G. and Thibon, J.-Y., J. Phys. A 39, 371 (2005)]. As the degrees of invariants increase, the alternative method proves to be particularly efficient.It is a recent observation that entanglement classification for qubits is closely related to local SL(2,C)-invariants including the invariance under qubit permutations [Dür, et al., Phys. Rev. A 62, 062314 (2000); Osterloh, A. and Siewert, J., Phys. Rev. A 72, 012337 (2005); O. Chterental and D. Ž. Ðoković, Linear Algebra Research Advances (Nova Science, Hauppauge, N.Y., 2007), Chap. 4, p. 133], which has been termed SL∗ invariance. In order to single out the SL∗ invariants, we analyze the SL(2,C)-invariants of four (five) qubits and decompose them into irreducible modules for the symmetric group S4 (S5) of qubit permutations. A classifying set of measures of genuine multipartite entanglement is given by the ideal of the algebra of SL∗-invariants vanishing on arbitrary product states. We find that low degree homogeneous components of this ideal can be constructed in full by using the approach introduced by Osterloh and Siewert [Phys. Rev. A 72, 012337 (2005); Int. J. Quant. Inf. 4, 531 (2006)]. Our analysis highlights an intimate connection between this latter procedure and the standard methods to create invariants, such as the Ω-process [Luque, J.-G. and Thibon, J.-Y., J. Phys. A 39, 371 (2005)]. As the degrees of invariants increase, the alternative method proves to be particularly efficient.

arXiv:0804.1661Journal of Mathematical PhysicsMar 1, 200993 citations

Entanglement classification of symmetric N-qubit States

Thierry Bastin, Stéphanie Krins, Pierre Mathonet +3 more

Jan 1, 20090 citations

Classification of Multipartite Entanglement of All Finite Dimensionality

Gilad Gour, Nolan R. Wallach

We provide a systematic classification of multiparticle entanglement in terms of equivalence classes of states under stochastic local operations and classical communication (SLOCC). We show that such a SLOCC equivalency class of states is characterized by ratios of homogenous polynomials that are invariant under local action of the special linear group. We then construct the complete set of all such SL-invariant polynomials (SLIPs). Our construction is based on Schur-Weyl duality and applies to any number of qudits in all (finite) dimensions. In addition, we provide an elegant formula for the dimension of the homogenous SLIPs space of a fixed degree as a function of the number of qudits. The expressions for the SLIPs involve in general many terms, but for the case of qubits we also provide much simpler expressions.We provide a systematic classification of multiparticle entanglement in terms of equivalence classes of states under stochastic local operations and classical communication (SLOCC). We show that such a SLOCC equivalency class of states is characterized by ratios of homogenous polynomials that are invariant under local action of the special linear group. We then construct the complete set of all such SL-invariant polynomials (SLIPs). Our construction is based on Schur-Weyl duality and applies to any number of qudits in all (finite) dimensions. In addition, we provide an elegant formula for the dimension of the homogenous SLIPs space of a fixed degree as a function of the number of qudits. The expressions for the SLIPs involve in general many terms, but for the case of qubits we also provide much simpler expressions.

arXiv:1304.7259Physical Review LettersAug 8, 201384 citations

A classification of entanglement in three-qubit systems

Carlos Sabín, Guillermo García Alcaine

arXiv:0707.1780The European Physical Journal DJun 5, 2008218 citations

Classification scheme of pure multipartite states based on topological phases

Markus Johansson, Marie Ericsson, Erik Sjöqvist +1 more

We investigate the connection between the concept of affine balancedness (a-balancedness) introduced by M. Johansson et al. [Phys. Rev. A 85, 032112 (2012)] and polynomial local SU invariants and the appearance of topological phases, respectively. It is found that different types of a-balancedness correspond to different types of local SU invariants analogously to how different types of balancedness, as defined by A. Osterloh and J. Siewert, [New J. Phys. 12, 075025 (2010)], correspond to different types of local special linear (SL) invariants. These different types of SU invariants distinguish between states exhibiting different topological phases. In the case of three qubits, the different kinds of topological phases are fully distinguished by the three-tangle together with one more invariant. Using this, we present a qualitative classification scheme based on balancedness of a state. While balancedness and local SL invariants of bidegree $(2n,0)$ classify the SL-semistable states [A. Osterloh and J. Siewert, New J. Phys. 12, 075025 (2010); O. Viehmann et al., Phys. Rev. A 83, 052330 (2011)], a-balancedness and local SU invariants of bidegree $(2n\ensuremath{-}m,m)$ give a more fine-grained classification. In this scheme, the a-balanced states form a bridge from the genuine entanglement of balanced states, invariant under the SL group, towards the entanglement of unbalanced states characterized by U invariants of bidegree $(n,n)$ . As a byproduct, we obtain generalizations to the W state, i.e., states that are entangled, but contain only globally distributed entanglement of parts of the system.We investigate the connection between the concept of affine balancedness (a-balancedness) introduced by M. Johansson et al. [Phys. Rev. A 85, 032112 (2012)] and polynomial local SU invariants and the appearance of topological phases, respectively. It is found that different types of a-balancedness correspond to different types of local SU invariants analogously to how different types of balancedness, as defined by A. Osterloh and J. Siewert, [New J. Phys. 12, 075025 (2010)], correspond to different types of local special linear (SL) invariants. These different types of SU invariants distinguish between states exhibiting different topological phases. In the case of three qubits, the different kinds of topological phases are fully distinguished by the three-tangle together with one more invariant. Using this, we present a qualitative classification scheme based on balancedness of a state. While balancedness and local SL invariants of bidegree $(2n,0)$ classify the SL-semistable states [A. Osterloh and J. Siewert, New J. Phys. 12, 075025 (2010); O. Viehmann et al., Phys. Rev. A 83, 052330 (2011)], a-balancedness and local SU invariants of bidegree $(2n\ensuremath{-}m,m)$ give a more fine-grained classification. In this scheme, the a-balanced states form a bridge from the genuine entanglement of balanced states, invariant under the SL group, towards the entanglement of unbalanced states characterized by U invariants of bidegree $(n,n)$. As a byproduct, we obtain generalizations to the W state, i.e., states that are entangled, but contain only globally distributed entanglement of parts of the system.

arXiv:1307.6993Physical Review AJan 21, 201416 citations

(2n,0)

classify the SL-semistable states [A. Osterloh and J. Siewert, New J. Phys. 12, 075025 (2010); O. Viehmann et al., Phys. Rev. A 83, 052330 (2011)], a-balancedness and local SU invariants of bidegree $(2n\ensuremath{-}m,m)$ give a more fine-grained classification. In this scheme, the a-balanced states form a bridge from the genuine entanglement of balanced states, invariant under the SL group, towards the entanglement of unbalanced states characterized by U invariants of bidegree

(n,n)

. As a byproduct, we obtain generalizations to the W state, i.e., states that are entangled, but contain only globally distributed entanglement of parts of the system.