  We study the dynamics of two identical atoms resonantly coupled to a
single-mode cavity under practical feedback control, and focus on the detection
inefficiency. The entanglement is induced to vanish in finite time by the
inefficiency of detection. Counterintuitively, the asymptotic entanglement and
quantum discord can be increased by the inefficiency of detection. The noise of
detection triggers control field to create entanglement and discord when no
photon are emitted from the atoms. Furthermore, sudden change happens to the
dynamics of entanglement.
