  We compute the bulk entanglement entropy of a massive scalar field in a
Poincare AdS with the Dirichlet and Neumann boundary condition when we trace
out a half space. Moreover, by taking into account the quantum back reaction to
the minimal surface area, we calculate how much the entanglement entropy
changes under a double-trace deformation of a holographic CFT. In the AdS3/CFT2
setup, our result agrees with the known result in 2d CFTs. In higher
dimensions, our results offer holographic predictions.
