  We construct an optimal state merging protocol by adapting a
recently-discovered optimal entanglement distillation protcol [Renes and
Boileau, Phys. Rev. A . 73, 032335 (2008)]. The proof of optimality relies only
on directly establishing sufficient "amplitude" and "phase" correlations
between Alice and Bob and not on usual techniques of decoupling Alice from the
environment. This strengthens the intuition from quantum error-correction that
these two correlations are all that really matter in two-party quantum
information processing.
