Dynamically Driven Irreversibility in Many Body Quantum Systems: An   experimental approach
  The NMR technique allows one to create a non-equilibrium local polarization and to detect its later evolution. By a change of the sign of the effective dipolar Hamiltonian, the apparently diffusive dynamics is reverted, generating a polarization echo (PE). This echo attenuates as a function of the time $t_R$ elapsed until the dynamics is reverted. We report a set of experiments where we slow down the dipolar dynamics showing that it controls this irreversibility. In cobaltocene, a cross over from Gaussian to exponential PE attenuation is found; in ferrocene the exponential regime is not reached. We conclude that many-body quantum systems have intrinsic instabilities, which amplify the environment fluctuations and hinder their backward evolution. 
Gonzalo Usaj, Horacio M. Pastawski, and Patricia R. Levstein