  We derive a general quantum exchange fluctuation theorem for multipartite
systems with arbitrary coupling strengths by taking into account the
informational contribution of the back-action of the quantum measurements,
which contributes to the increase in the von-Neumann entropy of the quantum
system. The resulting second law of thermodynamics is tighter than the
conventional Clausius inequality. The derived bound is the quantum mutual
information of the conditional thermal state, which is a thermal state
conditioned on the initial energy measurement. These results elucidate the role
of quantum correlations in the heat exchange between multiple subsystems.
