  It is a folklore result in arithmetic quantum chaos that quantum unique
ergodicity on the modular surface with an effective rate of convergence follows
from subconvex bounds for certain triple product $L$-functions. The physical
space manifestation of this result, namely the equidistribution of mass of
Hecke-Maass cusp forms, was proven to follow from subconvexity by Watson,
whereas the phase space manifestation of quantum unique ergodicity has only
previously appeared in the literature for Eisenstein series via work of
Jakobson. We detail the analogous phase space result for Hecke-Maass cusp
forms. The proof relies on the Watson-Ichino triple product formula together
with a careful analysis of certain archimedean integrals of Whittaker
functions.
