Occurrence of dynamic irreversibility in multi-body quantum systems: A test employing nuclear magnetic resonance

The NMR technique allows to create a non-equilibrium local polarization and to detect its later evolution. Besides, it is possible to change the sign of the effective dipolar Hamiltonian and therefore retrace an apparently di ffusive dynamics leading to a polarization echo. Our experiments in polycry stalline samples of (C5H5)Mn(CO)(3) and (C5H5)(2)Fe showed that those echoe s attenuate as function of the time elapsed until the dynamics is reverted. In the former, a strong irreversible quadrupolar interaction (non inverted ), produces an exponential decay. The latter has strong many-body interacti ons (reversible) whose quasi-chaotic dynamics has a local instability sensi tive to the presence of small residual interactions (non-inverted). Thus an irreversible Gaussian decay appears. Numerical solutions of model systems agree with this hypothesis. To control the dynamical parameters we applied to structurally similar crystals: (C5H5)(2)Fe and (C5H5)(2)Co, a pulse sequ ence devised ad-hoc. It limits the complexity of the dynamical state for ea ch t(R), slowing down its contribution to the attenuation and revealing the presence of an eventual underlying source of irreversibility. For (C5H5)(2 )Co an exponential decay [attributable to the magnetism of the Co(II)] emer ges when the dynamics is sufficiently reduced, while for (C5H5)(2)Fe the at tenuation remains Gaussian. This shows that irreversibility is controlled b y the reversible dynamics.