  We consider the Aharonov-Bohm effect on entanglement entropy for one interval
in (1+1) dimensional conformal field theory on a one dimensional ring. The
magnetic field is confined inside the ring, i.e. there is a Wilson loop on the
ring. The Aharonov-Bohm phase factor which is proportional to the Wilson loop
is represented as insertion of twist operators. We compute exactly the Renyi
entropy from a four point function of twist operators in a free charged scalar
field.
