  We investigate how to effectively preserve the entanglement between two
noninteracting multilevel oscillators coupled to a common reservoir under
non-ideal pulse control. A universal characterization using fidelity is
developed for the behavior of the system based on Nakajima-Zwanzig projection
operator technique. Our analysis includes the validity of the approximation
method and the decoherence-suppression by the non-ideal pulse control. The
power of our strategy for protecting entanglement is numerically tested,
showing potential applications for quantum information processing.
