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Coherent quantum dynamics in steady-state manifolds of strongly dissipative systems

It has been recently realized that dissipative processes can be harnessed and exploited to the end of coherent quantum control and information processing. In this spirit we consider strongly dissipative quantum systems admitting a non-trivial manifold of steady states. We show how one can enact adiabatic coherent unitary manipulations e.g., quantum logical gates, inside this {steady-state} manifold by adding a weak, time-rescaled, Hamiltonian term into the system's Liouvillian. The effective long-time dynamics is governed by a projected Hamiltonian which results from the interplay between the weak unitary control and the fast relaxation process. The leakage outside the {steady-state} manifold entailed by the Hamiltonian term is suppressed by an environment-induced symmetrization of the dynamics. We present applications to quantum-computation in decoherence-free subspaces and noiseless subsystems and numerical analysis of non-adiabatic errors.