paper

Entanglement negativity and topological order

arXiv:1306.5711 · doi:10.1103/PhysRevA.88.042318

Abstract

We use the entanglement negativity, a measure of entanglement for mixed states, to probe the structure of entanglement in the ground state of a topologically ordered system. Through analytical calculations of the negativity in the ground state(s) of the toric code model, we explicitly show that the entanglement of a region and its complement is the sum of two types of contributions. The first type of contributions consists of \textit{boundary entanglement}, which we see to be insensitive to tracing out the interior of and . It therefore entangles only degrees of freedom in and that are close to their common boundary. As it is well-known, each boundary contribution is proportional to the size of the relevant boundary separating and and it includes an additive, universal correction. The second contribution appears only when and are non-contractible regions (e.g. on a torus) and it consists of long-range entanglement, which we see to be destroyed when tracing out a non-contractible region in the interior of or . Only the long-range contribution to the entanglement may depend on the specific ground state under consideration.

14 pages, 5 figures (discussion enlarged) -- results closely related to C. Castelnovo, arXiv:1306.4990

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