We study origin, parameter optimization, and thermodynamic efficiency of isothermal
rocking ratchets based on fractional subdiffusion within a generalized non-Markovian
Langevin equation approach. A corresponding multi-dimensional Markovian embedding dynamics
is realized using a set of auxiliary Brownian particles elastically coupled to the central
Brownian particle (see video on the journal web site). We show that anomalous subdiffusive
transport emerges due to an interplay of nonlinear response and viscoelastic effects for
fractional Brownian motion in periodic potentials with broken space-inversion symmetry and
driven by a time-periodic field. The anomalous transport becomes optimal for a
subthreshold driving when the driving period matches a characteristic time scale of
interwell transitions. It can also be optimized by varying temperature, amplitude of
periodic potential and driving strength. The useful work done against a load shows a
parabolic dependence on the load strength. It grows sublinearly with time and the
corresponding thermodynamic efficiency decays algebraically in time because the energy
supplied by the driving field scales with time linearly. However, it compares well with
the efficiency of normal diffusion rocking ratchets on an appreciably long time scale.