  For a locally compact quantum group $\mathbb{G}$, consider the convolution
action of a quantum probability measure $\mu$ on $L_\infty(\mathbb{G})$. As
shown by Junge--Neufang--Ruan, this action has a natural extension to a Markov
map on $\mathcal{B}(L_2(\mathbb{G}))$. We prove that the Poisson boundary of
the latter can be realized concretely as the von Neumann crossed product of the
Poisson boundary associated with $\mu$ under the action of $\mathbb{G}$ induced
by the coproduct. This yields an affirmative answer, for general locally
compact quantum groups, to a problem raised by Izumi (2004) in the commutative
situation, in which he settled the discrete case, and unifies earlier results
of Jaworski, Neufang and Runde.
