Quantum dynamics of excitations and decoherence in many-spin systems detected with Loschmidt echoes: its relation to their spreading through the Hilbert space

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

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

ROYAL SOC

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

1364-503X

n this work, we overview time-reversal nuclear magnetic resonance (NMR) experiments in manyspin systems evolving under the dipolar Hamiltonian. The Loschmidt echo (LE) 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 of the manybodystate is directly monitored here experimentally by encoding the multiple quantum coherences. This enables a spin counting procedure, giving informationon the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two samples representing different spin systems withcoupled networks were used in the experiments. Protons in polycrystalline ferrocene corresponds to an infinite network. By contrast, the liquid crystalMBBA in the nematic mesophase represents a finite proton system with a hierarchical set of couplings. A close connection was established between