Entanglement in the presence of superselection rules

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  • 16 April 2003
Abstract
We quantify bipartite entanglement in the presence of general superselection rules (SSRs). These rules limit the allowed operations in a bipartite setting and thus place powerful constraints on quantum information processing (QIP). We show that ensemble QIP where elements in the ensemble are not individually addressable is subject to the SSR associated with the symmetric group (the group of permutations of elements). We prove that even for an ensemble comprising many pairs of qubits, each pair described by a pure Bell state, the entanglement per element in the presence of this SSR goes to zero for a large number of elements.

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