  It was shown [New J. Phys. 17, 103037 (2015)] that large and robust
entanglement between two different mechanical resonators could be achieved,
either dynamically or in the steady state, in an optomechanical system in which
the two mechanical resonators are coupled to a single cavity mode driven by a
suitably chosen two-tone field. An important limitation of the scheme is that
the cavity decay rate must be much smaller than the two mechanical frequencies
and their difference. Here we show that the entanglement can be remarkably
enhanced, and the validity of the scheme can be largely extended, by adding a
coherent feedback loop that effectively reduces the cavity decay rate.
