  We present a novel replica trick that computes the relative entropy of two
arbitrary states in conformal field theory. Our replica trick is based on the
analytic continuation of partition functions that break the replica Z_n
symmetry. It provides a method for computing arbitrary matrix elements of the
modular Hamiltonian corresponding to excited states in terms of correlation
functions. We show that the quantum Fisher information in vacuum can be
expressed in terms of two-point functions on the replica geometry. We perform
sample calculations in two-dimensional conformal field theories.
