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arXiv · 1007.0968

On the ring of local polynomial invariants for a pair of entangled qubits

Vladimir Gerdt·Arsen Khvedelidze·Yuri Palii
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Abstract

The entanglement characteristics of two qubits are encoded in the invariants of the adjoint action of SU(2) x SU(2) group on the space of density matrices defined as the space of positive semi-definite Hermitian matrices. The corresponding ring of polynomial invariants is studied. The special integrity basis for this ring is described and constraints on its elements due to the positive semi-definiteness of density matrices are given explicitly in the form of polynomial inequalities. The suggested basis is characterized by the property that only a minimal number of invariants, namely two primary invariants of degree 2, 3 and one secondary invariant of degree 4 appearing in the Hironaka decomposition of the ring are subject to the polynomial inequalities.

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Vladimir Gerdt, Arsen Khvedelidze, Yuri Palii. 2010-07-06. On the ring of local polynomial invariants for a pair of entangled qubits. https://arxiv.org/abs/1007.0968

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