Topological entanglement and hyperbolic volume

Abstract

The entanglement entropy of many quantum systems is difficult to compute in general. They are obtained as a limiting case of the Rényi entropy of index m, which captures the higher moments of the reduced density matrix. In this work, we study pure bipartite states associated with S3 complements of a two-component link which is a connected sum of a knot K and the Hopf link. For this class of links, the Chern-Simons theory provides the necessary setting to visualise the m-moment of the reduced density matrix as a three-manifold invariant Z(MKm), which is the partition function of MKm. Here MKm is a closed 3-manifold associated with the knot Km, where Km is a connected sum of m-copies of K(i.e., K#K . . . #K) which mimics the well-known replica method. We analayse the partition functions Z(MKm) for SU(2) and SO(3) gauge groups, in the limit of the large Chern-Simons coupling k. For SU(2) group, we show that Z(MKm) can grow at most polynomially in k. On the contrary, we conjecture that Z(MKm) for SO(3) group shows an exponential growth in k, where the leading term of ln Z(MKm) is the hyperbolic volume of the knot complement S3\Km. We further propose that the Rényi entropies associated with SO(3) group converge to a finite value in the large k limit. We present some examples to validate our conjecture and proposal.