TITLE: Symplectic Koopmanism
QUESTION [5 upvotes]: Let $(M, \omega)$ be a $2n$-dimensional symplectic manifold and let $L_2(M,|\omega^n|)$ be the Hilbert space of complex-valued functions on $M$ that are square integrable with respect to the Liouville measure. 
A classical (but still wonderful) remark due to Koopman is that given a measure preserving map $\phi: M \rightarrow M$, the operator
$$
U_\phi : L_2(M,|\omega^n|) \longrightarrow L_2(M,|\omega^n|)
$$
defined by $f \mapsto f \circ \phi$ is unitary. The operator $U_\phi$ is sometimes called the Koopman operator of the map $\phi$. Since symplectomorphisms are measure preserving, it seems natural to ask the following
Vague question. Is there anything at all particular about Koopman operators of symplectomorphisms?

REPLY [2 votes]: The Koopman operator is bracket preserving with respect to the canonical Poisson bracket on $C^{\infty}(M)$.  Formally, this implies the dual operator (the Frobenius-Perron operator) is a Poisson automorphism with respect to the Lie-Poisson structure on $\bigwedge^{2n}(M)$.