Universal dynamical decoupling of multiqubit states from environment

We study the dynamical decoupling of multiqubit states from environment. For a system of m qubits, the nested Uhrig dynamical decoupling (NUDD) sequence can efficiently suppress generic decoherence induced by system-environment interaction to order N using (N+1)^2m pulses. We prove that the NUDD sequence is universal, i.e., it can restore the coherence of m-qubit quantum system independent of the details of system-environment interaction. We also construct a general mapping between dynamical decoupling problems and discrete quantum walks in certain functional spaces.