Quantum variance on quaternion algebras, III

We determine the asymptotic quantum variance of microlocal lifts of Hecke--Maass cusp forms on the arithmetic compact hyperbolic surfaces attached to maximal orders in quaternion algebras. Our result extends those of Luo--Sarnak--Zhao concerning the non-compact modular surface. The results of this article's prequel (which involved the theta correspondence, Rallis inner product formula and equidistribution of translates of elementary theta functions) reduce the present task to some local problems over the reals involving the construction and analysis of microlocal lifts via integral operators on the group. We address these here using an analytic incarnation of the method of coadjoint orbits.