Long-lived selective spin echoes in dipolar solids under periodic and aperiodic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>π</mml:mi></mml:math>-pulse trains

Ridge, Clark D.; O’Donnell, Lauren; Walls, Jamie D.

doi:10.1103/physrevb.89.024404

Cited by 6 publications

(1 citation statement)

References 41 publications

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“…3a–f), whereas under CP-Y (blue circles), the echo amplitude is rapidly reduced, owing to the limited available rf power resulting in deviation from the ideal hard pulses (see Supplementary Note 3). The contrasting behaviour of T 2 under alternating phase CP-X/Y has been observed in other systems 44–46,48 and has been attributed variably to spin locking 48,49 or stimulated echoes 50 . Here, we ascribe the increase of T 2 under CP-X to a form of pulsed spin locking arising from dipolar evolution during the finite-duration π -pulses 49 : our interpretation is based on the observation that the spin lock disappears for small pulse-to-cycle time ratios t π / t c (see Supplementary Note 2).…”

Section: Resultsmentioning

confidence: 83%

Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths

et al. 2019

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Coherence of solid state spin qubits is limited by decoherence and random fluctuations in the spin bath environment. Here we develop spin bath control sequences which simultaneously suppress the fluctuations arising from intrabath interactions and inhomogeneity. Experiments on neutral self-assembled quantum dots yield up to a five-fold increase in coherence of a bare nuclear spin bath. Numerical simulations agree with experiments and reveal emergent thermodynamic behaviour where fluctuations are ultimately caused by irreversible conversion of coherence into many-body quantum entanglement. Simulations show that for homogeneous spin baths our sequences are efficient with non-ideal control pulses, while inhomogeneous bath coherence is inherently limited even under ideal-pulse control, especially for strongly correlated spin-9/2 baths. These results highlight the limitations of self-assembled quantum dots and advantages of strain-free dots, where our sequences can be used to control the fluctuations of a homogeneous nuclear spin bath and potentially improve electron spin qubit coherence.

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Section: Resultsmentioning

confidence: 83%

Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths

et al. 2019

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Finite pulse effects in CPMG pulse trains on paramagnetic materials

Leskes

Grey

2015

Phys. Chem. Chem. Phys.

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The Carr-Purcell-Meiboom-Gill (CPMG) sequence is commonly used in high resolution NMR spectroscopy and in magnetic resonance imaging for the measurement of transverse relaxation in systems that are subject to diffusion in internal or external gradients and is superior to the Hahn echo measurement, which is more sensitive to diffusion effects. Similarly, it can potentially be used to study dynamic processes in electrode materials for lithium ion batteries. Here we compare the (7)Li signal decay curves obtained with the CPMG and Hahn echo sequences under static conditions (i.e., in the absence of magic angle spinning) in paramagnetic materials with varying transition metal ion concentrations. Our results indicate that under CPMG pulse trains the lifetime of the (7)Li signal is substantially extended and is correlated with the strength of the electron-nuclear interaction. Numerical simulations and analytical calculations using Floquet theory suggest that the combination of large interactions and a train of finite pulses, results in a spin locking effect which significantly slows the signal's decay. While these effects complicate the interpretation of CPMG-based investigations of diffusion and chemical exchange in paramagnetic materials, they may provide a useful approach to extend the signal's lifetime in these often fast relaxing systems, enabling the use of correlation experiments. Furthermore, these results highlight the importance of developing a deeper understanding of the effects of the large paramagnetic interactions during multiple pulse experiments in order to extend the experimental arsenal available for static and in situ NMR investigations of paramagnetic materials.

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Breakdown of linear response theory under low-power excitation in NMR. II. The case of “long-lived” signals in homogeneously broadened dipolar spin systems

Gong

Walls

2018

The Journal of Chemical Physics

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In this work, the previous linear response theory developed to describe low-power, radiofrequency (RF) excitation in inhomogeneously broadened spin systems [Z. Gong and J. D. Walls, J. Chem. Phys. 145, 164201 (2016)] is applied to the problem of low-power excitation in homogeneously broadened dipolar spin systems when the strength of the RF pulse, νRF, is much less than the homogeneous linewidth, Δν12. Application of a low-power pulse for a time Tp with a nominal flip-angle of Θ generates a broad signal with a “dip” at the RF transmitter frequency that deepens with increasing Θ. When a delay is placed before signal acquisition, only a negative, “long-lived” signal from the narrow “dip” remains. If a πX-pulse is applied after low-power excitation, a “long-lived” signal lasting a time t ≈ Tp after the πX-pulse is generated where dephasing due to B0 inhomogeneity, anisotropic bulk magnetic susceptibility, and chemical shift anisotropy is refocused while dephasing due to nonzero chemical shift differences is only partially refocused. Contrary to previous observations, experiments in powdered hexamethylbenzene demonstrate that these “long-lived” signals can exist even in the absence of nonzero chemical shift differences. Additional experimental demonstrations in powdered and single-crystalline adamantane and ferrocene samples are also presented.

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

Cited by 6 publications

References 41 publications

Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths

Pulse control protocols for preserving coherence in dipolar-coupled nuclear spin baths

Finite pulse effects in CPMG pulse trains on paramagnetic materials

Breakdown of linear response theory under low-power excitation in NMR. II. The case of “long-lived” signals in homogeneously broadened dipolar spin systems

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