  A method for solving the problem of efficient population transfer from the
ground to some excited state by available technical means (varying resonator
length) is proposed. We consider a mixture of similar quantum systems
distributed in a stationary gas flow in the resonator with variable resonator
length, which implements tailored laser field close to the optimal one. In
difference from previous works, in this work piezoelectric transducer (PZT; or
actuator) is used as mean of control to manipulate variable resonator length.
The external actions are optimized to selectively prepare different stationary
states of different species which are then separated using their diffusion with
rates which differ due to different masses. This system provides an example of
the general problem of optimizing states of distributed systems with stationary
gas flow with diffusion.
