  In this work, we perform a series of phonon counting measurement with
different methods in a 3-mode optomechanical system, and we compare the
difference of the entanglement after measurement. In this article we focus on
the two cases: imperfect measurement and on-off measurement. We find that
whatever measurement you take, the entanglement will increase. The size of
entanglement enhancement is the largest in perfect measurement, second in the
imperfect measurement, and it is not obvious in the on-off measurement. We are
sure that the more precise measurement information, the larger entanglement
concentration.
