  We discuss an efficient numerical scheme for the recursive filtering of
diffusive quantum stochastic master equations. We show that the resultant
quantum trajectory is robust and may be used for feedback based on inefficient
measurements. The proposed numerical scheme is amenable to approximation, which
can be used to further reduce the computational burden associated with
calculating quantum trajectories and may allow real-time quantum filtering. We
provide a two-qubit example where feedback control of entanglement may be
within the scope of current experimental systems.
