  Dynamical decoupling can enforce a symmetry on the dynamics of an open
quantum system. Here we develop an efficient dynamical-decoupling-based
strategy to create the decoherence-free subspaces (DFSs) for a set of qubits by
optimally transferring the states of these qubits. We design to transfer the
state of each qubit to all of the other qubits in an optimal and efficient
manner, so as to produce an effective collective-type noise for all qubits.
This collective pseudo-noise is essentially derived from arbitrarily
independent real baths and needs only nearest-neighbor state transfers for its
implementation. Moreover, our scheme requires only N steps to produce the
effective collective-type noise for a system of N qubits. It provides an
experimentally feasible and efficient approach to achieving the DFSs for
encoding the protected logical qubits.
