Optimized dynamical decoupling for time-dependent Hamiltonians

The validity of optimized dynamical decoupling (DD) is extended to analytically time-dependent Hamiltonians. As long as an expansion in time is possible, the time dependence of the initial Hamiltonian does not affect the efficiency of optimized dynamical decoupling (UDD, Uhrig DD). This extension provides the analytic basis for (i) applying UDD to effective Hamiltonians in time-dependent reference frames, for instance in the interaction picture of fast modes and for (ii) its application in hierarchical DD schemes with pi pulses about two perpendicular axes in spin space to suppress general decoherence, i.e. longitudinal relaxation and dephasing.