Investigation of Relaxation Processes in the Multi-Pulse NMR Experiments

Long-lived coherence in driven spin systems: from two to infinite spatial dimensions

“…(1) The presence of long-time tails along the z-axis, which is perpendicular to the driving field, implies that the fundamental process for establishing long-time tails of the magnetization response is not spin locking [2,3] as may appear in analogy with other similar effects [9,10,39,42]. Our results seem to suggest that the origin of the long-lived coherences is primarily kinematic; it may arguably also involve many-body localization [4,22], transient prethermal regime [5,43,44], or spin-glass like behaviour.…”

“…An alternative to extend the spin coherence time, which attracted much attention recently, is based on external periodic perturbations by π-pulses. Long-lived magnetization response far beyond the usual time T 2 [4][5][6][7][8] was observed in many-spin systems including NMR systems [9][10][11][12][13], optically trapped ions [14] and NV-centers [15]. It is established now that the above long-lived magnetization response is caused by pulse nonidealities [16,17].…”

“…Moreover, since the spatial dimension d determines the fluctuation properties of the interaction constants for disordered dipolar-coupled spins, varying d is a viable tool to study the still challenging issue of fluctuations and disorder for the emergence of the above non-equilibrium steady states. Experimental and theoretical investigations of driven many-spin systems were mainly limited to the following values of d: the special case of one- dimensional d = 1 systems [19,20,[28][29][30][31][32][33][34][35] exhibiting spatio-temporal order, three-dimensional d = 3 systems in experiment [6,7,[9][10][11][12][13][14][15] and theory [16,36], and effectively infinite-dimensional d → ∞ systems [18,35,37].…”

On Quasistationary States in the Multipulse Spin‐Locking

“…It follows from (3), (4), (5), (9) and from the invariance of & with respect to a rotation through the angle 7t around the x-axis that the formal substitution p + + p -7t does not change est. Thus the average value (X,) = tr {e.tL?x}>itr A$: is invariant with respect to this substitution as well.…”

Theoretical investigations of quantum correlations in NMR multiple-pulse spin-locking experiments

“…resonance x-pulses locks the magnetization along axis x. Measurements of the magnetization in the windows between the pulses yield information about relaxation processes in solids [2,3]. It was shown experimentally that the multiple-pulse spin-locking experiment with the π/2-resonance pulses performs a long chain of echo signals with the amplitudes decaying on the time scale of T 2 ∼ T 2 /(ω loc τ ) 4 [4,5], where T 2 is the time of spin-spin relaxation, ω loc is the local dipolar frequency, and τ is proportional to the delay between two successive pulses. The theoretical confirmation of this result is given in [6].…”