Feed-forward control for quantum state protection against decoherence

We propose a scheme of feed-forward control and its reversal for protecting quantum state against decoherence. Before the noise channel our pre-weak measurement and feed-forward are simply to change the protected state into the state almost immune to the noise channel, and after the channel our reversed operations and post-weak measurements are simply to restore the protected state. Unlike most previous state protection schemes, ours only concerns the noise channel and does not care about the protected state. We show that our scheme can effectively protect unknown states, nonorthogonal states, and entangled states against amplitude damping noise. Our scheme has the merit of protecting quantum states against heavy amplitude damping noise, and can perfectly protect some specific nonorthogonal states in an almost deterministic way, which might find some applications in current quantum communication technology. And it is most important that our scheme is experimentally available with current technology.