  Atoms coupled to the same environment interfere with each other to yield
super- or sub-radiance. Specifically, atoms in subradiant states are promising
candidates for long-lifetime qubits and quantum memory because of the immunity
to the common environment. However, subradiant states can still be influenced
by local environments, which are incoherent for different atoms and cannot be
canceled out through interference. Here we propose to break this limit by
preparing a waveguide QED system in the non-Markovian regime, where the
ultra-small decay rate arises because of the retarded interaction. We further
show that similar effect occurs spontaneously by self-interference and can be
stressed by cooperative coupling.
