Beyond the coherent coupled channels description of nuclear fusion

New measurements of fusion cross sections at deep sub-barrier energies for the reactions O-16+Pb-204,Pb-208 show a steep but almost saturated logarithmic slope, unlike Ni-64-induced reactions. Coupled channels calculations cannot simultaneously reproduce these new data and above-barrier cross-sections with the same Woods-Saxon nuclear potential. It is argued that this highlights an inadequacy of the coherent coupled channels approach. It is proposed that a new approach explicitly including gradual decoherence is needed to allow a consistent description of nuclear fusion.