Solution
= Solution
The stationary solution of
$$
dq=-\nu q\,dt+\sqrt{\alpha\nu}\,dW
$$
is
$$
q(t)=\sqrt{\alpha\nu}\int_{-\infty}^te^{-\nu(t-u)}\,dW_u.
$$
It follows from the <Itô isometry> that
$$
\boxed{\langle q(t)q(t+\tau)\rangle
=\frac\alpha2e^{-\nu|\tau|}}.
$$
\b[Thus $q$ is zero-mean <colored noise> with correlation time $\nu^{-1}$. The equation $\dot x=\mu(-\lambda x+q)$ is an overdamped harmonic particle of mobility $\mu$ driven by that correlated random force.]