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

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