Experimental quantification of decoherence via the Loschmidt echo in a many spin

BULJUBASICH, LISANDRO; CLAUDIA M. SÁNCHEZ; AXEL D. DENTE; PATRICIA R. LEVSTEIN; ANA K. CHATTAH; HORACIO M. PASTAWSKI

JOURNAL OF CHEMICAL PHYSICS

AMER INST PHYSICS

Lugar: New York; Año: 2015 vol. 143 p. 164308 - 164308

0021-9606

We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence undera scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominatedProportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protonsin polycrystalline adamantane evolves through two steps of evolution characterized by the secularpart of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factorcan be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. Theexperimental results for the Loschmidt echoes showed a spreading of the decay rates that correlatedirectly to the scaling factors |k|, giving evidence that the decoherence is partially governed bythe coherent dynamics. The average Hamiltonian theory was applied to give an insight into thespin dynamics during the pulse sequence. The calculations were performed for every single radiofrequency block in contrast to the most widely used form. The first order of the average Hamiltoniannumerically computed for an 8-spin system showed decay rates that progressively decrease as thesecular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglectedby conventional calculations yielded an explanation for the ordering of the experimental decoherencerates. However, there is a strong overall decoherence observed in the experiments which isnot reflected by the theoretical results. The fact that the non-inverted terms do not account forthis effect is a challenging topic. A number of experiments to further explore the relation of thecomplete Hamiltonian with this dominant decoherence rate are proposed. C 2015 AIP PublishingLLC. [http://dx.doi.org/10.1063/1.4934221]