Generating Unexpected Spin Echoes in Dipolar Solids with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>Pulses

Li, Dale; Dementyev, Anatoly; Dong, Yanqun; Ramos, Rona; Barrett, Sean

doi:10.1103/physrevlett.98.190401

Cited by 41 publications

(56 citation statements)

References 18 publications

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“…(4), no long-lived echoes are predicted (as shown from simulations), and if H cs = 0, the effects of a CPMG(φ 1 , φ 2 ) pulse train is identical to that from the corresponding Hahn echo experiments in dipolar solids. As mentioned in the introduction, previous theories for observing long-lived echoes require imperfect π−pulses, either through consideration of dipolar evolution during the pulse 16,17 or due to field inhomogeneites that render the applied pulse imperfect [20][21][22] . While including H D during the pulse would definitely be needed if the interpulse spacing, 2τ , was comparable to the π−pulse time, t p = (2)].…”

Section: Theory and Numerical Simulationsmentioning

confidence: 99%

“…Such observations are reconfirmed in Figs There have been two main theoretical proposals to understand the long-lived spin echoes under CPMG pulse trains. One explanation, propounded by the Barrett group [16][17][18] , which we refer to in throughout the paper as the Barrett proposal, is that these long-lived echoes are a consequence of resonance offset and dipolar evolution during the π−pulse, i.e., the π−pulses cannot be treated as pure δ-pulses. Using average Hamiltonian theory 19 (AHT), these authors demonstrated that the CPMG(φ 1 , φ 2 ) generates an effective field that, depending on the π pulse phases, φ 1 and φ 2 , can spin-lock the magnetization after an initial π 2 X pulse; it was argued 17 that this effect was not equivalent to pulsed spin-locking.…”

Section: Introductionmentioning

confidence: 99%

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Long-lived selective spin echoes in dipolar solids under periodic and aperiodicπ-pulse trains

2014

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The application of Carr-Purcell-Meiboom-Gill (CPMG) π−trains for dynamically decoupling a system from its environment has been extensively studied in a variety of physical systems. When applied to dipolar solids, recent experiments have demonstrated that CPMG pulse trains can generate long-lived spin echoes. While there still remains some controversy as to the origins of these long-lived spin echoes under the CPMG sequence, there is a general agreement that pulse errors during the π−pulses are a necessary requirement. In this work, we develop a theory to describe the spin dynamics in dipolar coupled spin-1/2 system under a CPMG(φ1, φ2) pulse train, where φ1 and φ2 are the phases of the π−pulses. From our theoretical framework, the propagator for the CPMG(φ1, φ2) pulse train is equivalent to an effective "pulsed" spin-locking of single-quantum coherences with phase ± φ 2 −3φ 1 2 , which generates a periodic quasiequilibrium that corresponds to the long-lived echoes. Numerical simulations, along with experiments on both magnetically dilute, random spin networks found in C60 and C70 and in non-dilute spin systems found in adamantane and ferrocene, were performed and confirm the predictions from the proposed theory.

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Section: Theory and Numerical Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long-lived selective spin echoes in dipolar solids under periodic and aperiodicπ-pulse trains

2014

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“…In all the samples mentioned already, the spin-spin decay time measured with a Hahn echo sequence (T HE 2 ) [34] was about an order of magnitude longer than the FID characteristic time (T * 2 ), evidencing the line inhomogeneity. Magnetization tails have been observed in 29 Si, C 60 and Y 2 O 3 [13,41,42], in adamantane under 1 H decoupling [57] and indirectly in 31 P in EPR experiments [20].…”

Section: Long-lived Signalsmentioning

confidence: 96%

“…We summarize our own findings on anomalous long-lived echo signals [12,[41][42][43][44]. In particular, we emphasize the use of a simple stimulated echo sequence to discern whether one is in the presence of true long decoherence times or if the coherences are being saved as polarization and then recovered.…”

Section: Introductionmentioning

confidence: 99%

Storage of quantum coherences as phase-labelled local polarization in solid-state nuclear magnetic resonance

Franzoni

Acosta

Pastawski

et al. 2012

Phil. Trans. R. Soc. A.

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Nuclear spins are promising candidates for quantum information processing because their good isolation from the environment precludes the rapid loss of quantum coherence. Many strategies have been developed to further extend their decoherence times. Some of them make use of decoupling techniques based on the Carr-Purcell and Carr-PurcellMeiboom-Gill pulse sequences. In many cases, when applied to inhomogeneous samples, they yield a magnetization decay much slower than that of the Hahn echo. However, we have proved that these decays cannot be associated with longer decoherence times, as coherences remain frozen. They result from coherences recovered after their storage as local polarization and thus they can be used as memories. We show here how this freezing of the coherent state, which can subsequently be recovered after times longer than the natural decoherence time of the system, can be generated in a controlled way with the use of field gradients. A similar behaviour of homogeneous samples in inhomogeneous fields is demonstrated. It is emphasized that the effects of inhomogeneities in solid-state nuclear magnetic resonance, independently of their origin, should not be disregarded, as they play a crucial role in multipulse sequences.

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“…Using expression (23) for the truncated dipolar Hamiltonian, it is possible to split this expression in two parts:…”

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confidence: 99%

Controlling the dipole-dipole interaction using NMR composite rf pulses

Baudin

2014

The Journal of Chemical Physics

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I describe composite pulses during which the average dipolar interactions within a spin ensemble are controlled while realizing a global rotation. The construction method used is based on the average Hamiltonian theory and rely on the geometrical properties of the spin-spin dipolar interaction only. I present several such composite pulses robust against standard experimental defects in NRM: static or radio-frequency field miscalibration, fields inhomogeneities. Numerical simulations show that the magic sandwich pulse sequence, a pulse sequence that reverse the average dipolar field while applied, is plagued by defects originating from its short initial and final π/2 radio-frequency pulses. Using the magic composite pulses instead of π/2 pulses improves the magic sandwich effect. A numerical test using a classical description of NMR allows to check the validity of the magic composite pulses and estimate their efficiency.

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Generating Unexpected Spin Echoes in Dipolar Solids withπPulses

Cited by 41 publications

References 18 publications

Long-lived selective spin echoes in dipolar solids under periodic and aperiodicπ-pulse trains

Long-lived selective spin echoes in dipolar solids under periodic and aperiodicπ-pulse trains

Storage of quantum coherences as phase-labelled local polarization in solid-state nuclear magnetic resonance

Controlling the dipole-dipole interaction using NMR composite rf pulses

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