  Quantum mechanics describes the unitary time evolution of closed systems. In
practice, every quantum system interacts with the environment leading to an
irreversible loss of coherence. The Spin-Boson model (SBM) is central to the
understanding of the fundamental process of decoherence of a two-state quantum
system interacting with a bosonic heat bath but the nature of transient
dynamics in the presence of hybrid diagonal and off-diagonal system-bath
interactions remains largely unexplored. Here, we investigate how the hybrid
system-bath interactions of an Ohmic environment induce localization in the
bias-free SBM. For strong coupling to the environment, localization is strongly
affected by a dynamically generated bias via the renormalization of the
tunneling amplitude. We find that counteractive effects of Hamiltonian
parameters on non-exponential short-time dynamics and long-time population
equilibration can lead to a separation of timescales and non-equilibrium
quantum coherent dynamics that can persist even for ultra-strong system-bath
interaction. The findings offer novel opportunities to exploit coherence as a
resource in quantum devices operating in the ultra-strong coupling regime.
