  Suppose that two distant parties Alice and Bob share an entangled state
$\rho_{AB}$, and they want to exchange the subsystems of $\rho_{AB}$ by local
operations and classical communication (LOCC). In general, this LOCC task (i.e.
the LOCC transformation of $\rho_{AB} \to V\rho_{AB} V$ with $V$ being a swap
operator) is impossible deterministically, but becomes possible
probabilistically. In this paper, we study how the optimal probability is
related to the amount of entanglement in the framework of positive partial
transposed (PPT) operations, and numerically show a remarkable class of states
whose probability is the smallest among every state in two quantum bits.
