Low perturbation limit decoherence analyzed by scaling the Double Quantum Hamiltonian

SÁNCHEZ, C. M.; PASTAWSKI, H. M.; CHATTAH, A. K.

Journal of Magnetic Resonance Open

Elsevier

Lugar: Amsterdam; Año: 2023

2666-4410

By varying the magnitude of the effective interaction between spins in relation to the perturbations,we study the decoherence behavior in a connected proton system. Making use of the Magnusexpansion, we introduce a NMR pulse sequence that generates an average Hamiltonian with DoubleQuantum terms multiplied by a scaling factor, δ, with the possibility to take positive and negativevalues. The performance of the pulse sequence for different values of the scaling factors was validatedin polycrystalline adamantane, by observing the evolution of the polarization. In order to observethe multiple quantum coherences, it is necessary to carry out a time reversal procedure, accessiblethanks to the possibility of changing the sign in the controlled Hamiltonian. The spin countingdevelops a characteristic growth in two species of clusters for the scaled time. The influence of thescaling factor on the reversibility was observed through the behavior of the Loschmidt echoes, whichdecayed faster as the scaling factor increases. From the analysis of dynamics and its reversibility,we extracted characteristic times for the spin diffusion, T2, the intrinsic decoherence decay, Tδ3 foreach scaling factor δ, and perturbation time scale, TΣ. Observing the dependence of reversibilityvs. perturbation rates, both normalized with the spin diffusion rate, we find that in the limit oflow perturbations, Tδ2 /T δ3 deviates from the linear dependence on Tδ2 /TΣ that corresponds to strongperturbation. The asymptotic value T2/T3 ≈ 0.15 as Tδ2 /TΣ vanishes, gives evidence that the mainsource of irreversibility is the intrinsic decoherence associated to the chaotic many-body dynamicsof the system.