Loschmidt echo as indicator of decoherence in many body spin systems.

C.M. SANCHEZ; P.R. LEVSTEIN; R. H. ACOSTA; A.K. CHATTAH

Angra dos Reis, Brasil

Congreso; 12th Nuclear Magnetic Resonance Users Meeting & 3rd Iberoamerican NMR Meeting.; 2009

In this work, we study the decoherence that occurs during the evolution of dipolar coupled nuclear spin systems using solid state Nuclear Magnetic Resonance (NMR). The decoherence processes lead to a loss of information that can be quantified through a Loschmidt echo (LE). The LEs are those generated by reverting the time evolution of a system. We focus on experimental implementations of several LEs as quantifiers of decoherence in many body spin systems by changing the sign of the Hamiltonians.LE Implementations with different Hamiltonians and different systems can provide information to differentiate intrinsic decoherence, i.e. that induced by the own interactions of the system, from that arising on experimental imperfections.     We probe the spin dynamics with two Hamiltonians, a rotated dipolar Hamiltonian, Hxx ~ (2IxjIxk- IzjIzk- IyjIyk), and a double quantum Hamiltonian HDQ ~ (I+jI+k + I-jI-k), on two spin systems: adamantane, that involves an infinite 1/2 spin network with only intermolecular dipolar interactions and the liquid crystal 5CB in the nematic phase, where only intramolecular dipolar interactions survive giving rise to a closed system of a finite number of spins. The spin dynamics are analyzed by comparing the evolution of Multiple Quantum Coherences (MQC). The experiments were performed using a Bruker Avance II spectrometer operating at a ¹H resonance frequency of 300.13 MHz at 300 K.