Quantum Dynamics of Excitations and Decoherence in Many-spin Sys- tems Detected with Loschmidt Echoes: its relation to their spreading through the Hilbert space

P. R. LEVSTEIN; A. K. CHATTAH; C. M. SÁNCHEZ; H. M. PASTAWSKI; L. BULJUBASICH

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL AND PHYSICAL SCIENCES

ROYAL SOC

Lugar: Londres; Año: 2016 vol. 374 p. 20150155 - 20150155

0080-4614

In this work we overview time-reversal NMR experiments in many-spinsystems evolving under the dipolar Hamiltonian. The Loschmidt echo in NMR is the signal of excitations which after evolving with a forward Hamiltonian is recovered by means of a backward evolution. The presence of non-diagonal terms in the non-equilibrium density matrix ofthe many-body state was directly monitored by experimentally encoding themultiple quantum coherences. This enabled a spin counting procedure, giving information on the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two spin systems with very different coupled networks were measured. Polycrystalline Ferrocene corresponds to an extquotedblleft infiniteextquotedblright network. The liquid crystal MBBA in the nematic mesophase, represents a finite system with a hierarchical set of couplings. A close connection was established between the LE decay and the spin counting measurements, confirming the hypothesis that the complexity of the system is driven by the coherent dynamics.