Understanding decoherence in the time reversal dynamics of dipolar coupled nuclear spins using NMR Loschmidt Echo.

A.K. CHATTAH; C. SÁNCHEZ; P.R. LEVSTEIN; R.H. ACOSTA

Biddeford, New England, EEUU

Conferencia; Gordon Research Conference in Magnetic Resonace; 2009

Gordon Research Conference

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 reversing 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 about the intrinsic decoherence, i.e. that induced by the own interactions of the system, and that arising on experimental imperfections.We probe the spin dynamics with two Hamiltonians, a rotated dipolar Hamiltonian, Hxx, and a double quantum Hamiltonian HDQ, on different spin systems: adamantane, that involves an infinite 1/2 spin network with only intermolecular dipolar interactions, 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, and polycrytalline ferrrocene where intra e inter molecular interactions are equally important.  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. Numerical simulations are performed.