A nuclear magnetic resonance answer to the Boltzmann-Loschmidt controversy?

A unique experimental tool to deepen into the Boltzmann-Loschmidt controver sy is provided by the NMR polarization echoes (PE). These appear when a loc al spin excitation, evolving with a many-body "diffusive" spin dynamics, is reversed. The attenuation of the PEs represents a progresive failure of th e quantum interferences to rebuild the local excitation. Our results indica te that, in the absence of detectable environmental interactions, the chara cteristic time of this attenuation is determined by the reversible dynamics itself, i.e., spin-spin interaction time. This supports the Boltzmann's hy pothesis of molecular "chaos". (C) 2000 Elsevier Science B.V. All rights re served.