nuclear magnetic resonance

Nat. Commun.: Local and bulk 13C hyperpolarization in nitrogen-vacancy-centred diamonds at variable fields and orientations

Posted on

Gonzalo A. Álvarez, Christian O. Bretschneider, Ran Fischer, Paz London, Hisao Kanda, Shinobu Onoda, Junichi Isoya, David Gershoni & Lucio Frydman

Nature Communications 6, 8456 (2015). doi:10.1038/ncomms9456

 

 
Combined Optical and Nuclear Magnetic Resonance (NMR) setup for hyperpolarizing nuclear spins in diamonds at room- temperature. During the polarization transfer phase, the entire single-crystal diamond (red in the picture) is irradiated with green laser light and microwaves underneath the NMR magnet at a low magnetic field. The hyperpolarized diamond is then shuttled into a high field superconducting magnet, for a directly detected NMR experiment on the 13C spins.Polarizing nuclear spins is of fundamental importance in biology, chemistry and physics. Methods for hyperpolarizing 13C nuclei from free electrons in bulk usually demand operation at cryogenic temperatures. Room temperature approaches targeting diamonds with nitrogen-vacancy centres could alleviate this need; however, hitherto proposed strategies lack generality as they demand stringent conditions on the strength and/or alignment of the magnetic field. We report here an approach for achieving efficient electron-13C spin-alignment transfers, compatible with a broad range of magnetic field strengths and field orientations with respect to the diamond crystal. This versatility results from combining coherent microwave- and incoherent laser-induced transitions between selected energy states of the coupled electron–nuclear spin manifold. 13C-detected nuclear magnetic resonance experiments demonstrate that this hyperpolarization can be transferred via first-shell or via distant 13Cs throughout the nuclear bulk ensemble. This method opens new perspectives for applications of diamond nitrogen-vacancy centres in nuclear magnetic resonance, and in quantum information processing.

 

Source: Local and bulk 13C hyperpolarization in nitrogen-vacancy-centred diamonds at variable fields and orientations : Nature Communications : Nature Publishing Group

 

Acquiring ensemble 13C polarization spectra for varying NV orientations with respect to B0. (a) Opto-NMR set-up and (b) detection sequence used in these experiments. During the polarization transfer phase, the entire single-crystal diamond is irradiated with laser light and MW underneath the NMR magnet at a low B0. The hyperpolarized diamond is then shuttled (in <1 s) into a 4.7-T superconducting magnet to directly detect its macroscopic 13C magnetization via a spin-echo sequence. The low B0 magnetic field is aligned to one of the nitrogen-vacancy-centre orientations (in red), while the other three orientations (in blue) subtend an angle of ≈109° with respect to the field. (c) Typical 13C polarization enhancement patterns observed by NMR as a function of the MW frequency ω with signals normalized with respect to the thermal 13C response at 4.7 T (inset). The left part of the plot corresponds the nuclear polarization generated by MW transitions for the aligned orientation (red circles), while the right part corresponds to nuclear polarization enhanced via the three non-aligned, equivalent orientations (blue circles). The ≈1:3 intensity ratio reflects the relative abundances of aligned and non-aligned sites in the diamond’s tetrahedral structure. In each of the patterns, the central peaks represent bulk nuclear hyperpolarization pumped via 13C spins coupled with hyperfine interactions lower than 20 MHz, while the outer peaks originate from first-shell 13Cs whose hyperfine splitting is ≈130 MHz (refs 26, 29). The antiphase structure of each of these peaks corresponds to the MW transitions and at one side of the central peaks, and to the state at the other side. The inset shows NMR spectra obtained for a thermally polarized sample, and at the maxima of the central peaks for the aligned and non-aligned orientations. p.p.m. refers to parts-per-million of the high-field NMR 13C resonance frequency, which in our case is 50.5 MHz.
Acquiring ensemble 13C polarization spectra for varying NV orientations with respect to B0. (a) Opto-NMR set-up and (b) detection sequence used in these experiments. During the polarization transfer phase, the entire single-crystal diamond is irradiated with laser light and MW underneath the NMR magnet at a low B0. The hyperpolarized diamond is then shuttled (in <1 s) into a 4.7-T superconducting magnet to directly detect its macroscopic 13C magnetization via a spin-echo sequence. The low B0 magnetic field is aligned to one of the nitrogen-vacancy-centre orientations (in red), while the other three orientations (in blue) subtend an angle of ≈109° with respect to the field. (c) Typical 13C polarization enhancement patterns observed by NMR as a function of the MW frequency ω with signals normalized with respect to the thermal 13C response at 4.7 T (inset). The left part of the plot corresponds the nuclear polarization generated by MW transitions for the aligned orientation (red circles), while the right part corresponds to nuclear polarization enhanced via the three non-aligned, equivalent orientations (blue circles). The ≈1:3 intensity ratio reflects the relative abundances of aligned and non-aligned sites in the diamond’s tetrahedral structure. In each of the patterns, the central peaks represent bulk nuclear hyperpolarization pumped via 13C spins coupled with hyperfine interactions lower than 20 MHz, while the outer peaks originate from first-shell 13Cs whose hyperfine splitting is ≈130 MHz. The inset shows NMR spectra obtained for a thermally polarized sample, and at the maxima of the central peaks for the aligned and non-aligned orientations. p.p.m. refers to parts-per-million of the high-field NMR 13C resonance frequency, which in our case is 50.5 MHz.

Science: Localization-delocalization transition in the dynamics of dipolar-coupled nuclear spins

Posted on

Nonequilibrium dynamics of many-body systems are important in many scientific fields. Here, we report the experimental observation of a phase transition of the quantum coherent dynamics of a three-dimensional many-spin system with dipolar interactions. Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we quench the interaction Hamiltonian to drive the evolution of the system. Depending on the quench strength, we then observe either localized or extended dynamics of the system coherence. We extract the critical exponents for the localized cluster size of correlated spins and diffusion coefficient around the phase transition separating the localized from the delocalized dynamical regime. These results show that NMR techniques are well suited to studying the nonequilibrium dynamics of complex many-body systems.

 

Gonzalo A. Álvarez (1), Dieter Suter (2), Robin Kaiser (3)

(1) Department of Chemical Physics, Weizmann Institute of Science, 76100, Rehovot, Israel.
(2) Fakultät Physik, Technische Universität Dortmund, D-44221, Dortmund, Germany.
(3) Institut Non-Linéaire de Nice, CNRS, Université de Nice Sophia Antipolis, 06560, Valbonne, France.

Science 349, 846 (2015)

DOI: 10.1126/science.1261160

 

scaling_localization-delocalization_transition
Time evolution of the cluster size of correlated spins K for different quench strengths (1-p) and finite-time scaling procedure. (A) Cluster-size K as a function of the time t after the quench. The unperturbed quenched evolution (black squares) shows a cluster-size K that grows as ∼t^(4.3) at long times (dashed line is a guide to the eye). The solid symbols show the points used for a finite-time scaling analysis, while the empty symbols do not belong to the long time regime (t < 0.3 ms). For the largest perturbation strengths p to the quench, localization effects are clearly visible by the saturation of the cluster size. (B and C) In these two panels, we present the finite-time scaling procedure. In (B), the rescaled and squared correlation length l^2= K^(2/3) as a function of the evolution time 1=t^(k_2) is plotted. In (C), the curves of (B) are rescaled horizontally by the scaling factor ξ(p) to obtain a universal scaling law.

 

localization-delocalization_transition
Scaling factor and critical exponents. Normalized scaling factor ξ(p) as a function of p (blue triangles). The red solid line is a fit to the blue triangles with a expression ξ(p) proportional to|p − p_c|^nu, the critical exponent is then nu= 0,42. The two insets show the distribution of coherence orders of the density matrix as a function of the evolution time t for two perturbation strengths, which correspond to a delocalized and localized regime, respectively. The corresponding scaling factors are indicated by the arrows.

via Localization-delocalization transition in the dynamics of dipolar-coupled nuclear spins.

PLoS ONE: Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI

Posted on Updated on

Noam Shemesh, Gonzalo A. Álvarez, Lucio Frydman

Published: July 21, 2015

DOI: 10.1371/journal.pone.0133201

Abstract

Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems – ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Ec​ho(NOGSE), can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length)^6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE’s ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions – where the ground truth can be determined from ancillary microscopy – corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE’s potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.

Citation: Shemesh N, Álvarez GA, Frydman L (2015) Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI. PLoS ONE 10(7): e0133201. doi:10.1371/journal.pone.0133201

Editor: Ichio Aoki, National Institute of Radiological Sciences, JAPAN

Received: November 25, 2014; Accepted: June 24, 2015; Published: July 21, 2015

Copyright: © 2015 Shemesh et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

 

via PLOS ONE: Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI.

 

Magnetic resonance virtual histology
Magnetic resonance virtual histology based on probing molecular diffusion in tissues. Non-uniform oscillating gradient spin-echo (NOGSE) sequences are applied to generate the magnetic resonance imaging (MRI) contrast. The compartment size distributions in a mouse corpus callosum are extracted highlighting the different anatomical regions.

Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance | J. Chem. Phys. (2014)

Posted on

Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance

Gonzalo A. Álvarez, Noam Shemesh and Lucio Frydman
J. Chem. Phys. 140, 084205 (2014); http://dx.doi.org/10.1063/1.4865335

Dynamical decoupling, a generalization of the original NMR spin-echo sequence, is becoming increasingly relevant as a tool for reducing decoherence in quantum systems. Such sequences apply non-equidistant refocusing pulses for optimizing the coupling between systems, and environmental fluctuations characterized by a given noise spectrum. One such sequence, dubbed Selective Dynamical Recoupling SDR [P. E. S. Smith, G. Bensky, G. A. Álvarez, G. Kurizki, and L. Frydman, Proc. Natl. Acad. Sci. 109, 5958 (2012)], allows one to coherently reintroduce diffusion decoherence effects driven by fluctuations arising from restricted molecular diffusion [G. A. Álvarez, N. Shemesh, and L. Frydman, Phys. Rev. Lett. 111, 080404 (2013)]. The fully-refocused, constant-time, and constant-number-of-pulses nature of SDR also allows one to filter out “intrinsic” T1 and T2 weightings, as well as pulse errors acting as additional sources of decoherence. This article explores such features when the fluctuations are now driven by unrestricted molecular diffusion. In particular, we show that diffusion-driven SDR can be exploited to investigate the decoherence arising from the frequency fluctuations imposed by internal gradients. As a result, SDR presents a unique way of probing and characterizing these internal magnetic fields, given an a priori known free diffusion coefficient. This has important implications in studies of structured systems, including porous media and live tissues, where the internal gradients may serve as fingerprints for the systems composition or structure. The principles of this method, along with full analytical solutions for the unrestricted diffusion-driven modulation of the SDR signal, are presented. The potential of this approach is demonstrated with the generation of a novel source of MRI contrast, based on the background gradients active in an ex vivo mouse brain. Additional features and limitations of this new method are discussed.

© 2014 AIP Publishing LLC

via Diffusion-assisted selective dynamical recoupling: A new approach to measure background gradients in magnetic resonance, J. Chem. Phys. 140, 084205 (2014); http://dx.doi.org/10.1063/1.4865335.

Selective dynamical recoupling (SDR) series of images and the corresponding ex-vivo mouse brain background gradients (central panel) derived from these data.
Selective dynamical recoupling (SDR) series of images and the corresponding ex-vivo mouse brain background gradients (central panel) derived from these data.

Quantum simulations of localization effects with dipolar interactions | Annalen der Physik – 2013

Posted on

Quantum simulations of localization effects with dipolar interactions

Gonzalo A. Álvarez, Robin Kaiser, Dieter Suter

Abstract:
Quantum information processing often uses systems with dipolar interactions. Here a nuclear spin-based quantum simulator is used to study the spreading of information in such a dipolar-coupled system. While the information spreads with no apparent limits in the case of ideal dipolar couplings, additional perturbations limit the spreading, leading to localization. In previous work [Phys. Rev. Lett. 104, 230403 (2010)], it was found that the system size reaches a dynamic equilibrium that decreases with the square of the perturbation strength. This work examines the impact of a disordered Hamiltonian with dipolar interactions. It shows that the expansion of the cluster of spins freezes in the presence of large disorder, reminiscent of Anderson localization of non-interacting waves in a disordered potential.

Keywords: spin dynamics;dipolar interaction;decoherence;localization;disorder;NMR;long range interactions;quantum information processing

Annalen der Physik
Special Issue on “Quantum Simulations“, featuring review papers written by last year’s Nobel Prize winners describing their foundational work (Wineland and Haroche). Issue edited by: Rainer Blatt, Immanuel Bloch, Ignacio Cirac, Peter Zoller.
Ann. Phys. 525, 833 (2013).
DOI: 10.1002/andp.201300096

© 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

via Quantum simulations of localization effects with dipolar interactions – Álvarez – 2013 – Annalen der Physik – Wiley Online Library.

Quantum simulations of localization effects with dipolar interactions - Álvarez - 2013 - Annalen der Physik - Wiley Online Library
Time evolution of the cluster-size of correlated spins starting from different initial sates. The experimental data is shown for two different perturbation strengths given in the legend. The solid black squares, red triangles and green rhombuses are evolutions from an uncorrelated initial state. Empty symbols start from an initial state with K0 correlated spins. The insets show the Multiple Quantum Coherence spectrum starting from K0 = 141 as a functions of time for a perturbation strength.

Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo NOGSE NMR | J. Magn. Reson. (2013)

Posted on

Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo NOGSE NMR

Noam Shemesh, Gonzalo A. Álvarez, Lucio Frydman.
Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.

J. Magn. Reson. 237, 49–62 (2013).

 

Highlights:
•NOGSE, a novel diffusion MR approach for measuring pore sizes, is presented and analyzed.
•NOGSE is based on a constant time and a constant number of oscillating gradients.
•Experiments on microstructural phantoms, spinal cords and brains, validate NOGSE.

Abstract:
Noninvasive measurements of microstructure in materials, cells, and in biological tissues, constitute a unique capability of gradient-assisted NMR. Diffusion–diffraction MR approaches pioneered by Callaghan demonstrated this ability; Oscillating-Gradient Spin-Echo OGSE methodologies tackle the demanding gradient amplitudes required for observing diffraction patterns by utilizing constant-frequency oscillating gradient pairs that probe the diffusion spectrum, Dω. Here we present a new class of diffusion MR experiments, termed Non-uniform Oscillating-Gradient Spin-Echo NOGSE, which dynamically probe multiple frequencies of the diffusion spectral density at once, thus affording direct microstructural information on the compartment’s dimension. The NOGSE methodology applies N constant-amplitude gradient oscillations; N − 1 of these oscillations are spaced by a characteristic time x, followed by a single gradient oscillation characterized by a time y, such that the diffusion dynamics is probed while keeping N − 1x + y ≡ TNOGSE constant. These constant-time, fixed-gradient-amplitude, multi-frequency attributes render NOGSE particularly useful for probing small compartment dimensions with relatively weak gradients – alleviating difficulties associated with probing Dω frequency-by-frequency or with varying relaxation weightings, as in other diffusion-monitoring experiments. Analytical descriptions of the NOGSE signal are given, and the sequence’s ability to extract small compartment sizes with a sensitivity towards length to the sixth power, is demonstrated using a microstructural phantom. Excellent agreement between theory and experiments was evidenced even upon applying weak gradient amplitudes. An MR imaging version of NOGSE was also implemented in ex vivo pig spinal cords and mouse brains, affording maps based on compartment sizes. The effects of size distributions on NOGSE are also briefly analyzed.

Keywords:
Restricted diffusion; Oscillating gradients; OGSE; Microstructure; Magnetic resonance imaging; CNS; Gradient echoes; Selective dynamical recoupling

Graphical abstract:

Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo NOGSE NMR

via Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo NOGSE NMR.

Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance | Phys. Rev. Lett. 111, 080404 (2013)

Posted on Updated on

Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance

Gonzalo A. Álvarez, Noam Shemesh, and Lucio Frydman
Department of Chemical Physics, Weizmann Institute of Science, Rehovot, 76100, Israel
Received 13 May 2013; published 20 August 2013

During recent years, dynamical decoupling (DD) has gained relevance as a tool for manipulating and interrogating quantum systems. This is particularly relevant for spins involved in nuclear magnetic resonance (NMR), where DD sequences can be used to prolong quantum coherences, or to selectively couple or decouple the effects imposed by random environmental fluctuations. In this Letter, we show that these concepts can be exploited to selectively recouple diffusion processes in restricted spaces. The ensuing method provides a novel tool to measure restriction lengths in confined systems such as capillaries, pores or cells. The principles of this method for selectively recoupling diffusion-driven decoherence, its standing within the context of diffusion NMR, extensions to the characterization of other kinds of quantum fluctuations, and corroborating experiments, are presented.

© 2013 American Physical Society

via Phys. Rev. Lett. 111, 080404 (2013): Coherent Dynamical Recoupling of Diffusion-Driven Decoherence in Magnetic Resonance.

arXiv: [1305.2794] Coherent dynamical recoupling of diffusion-driven decoherence in magnetic resonance.

Time evolution of the spin magnetization under CPMG (N = 8 pulses) and Hahn-echo sequences for spins diffusing in a restricted space (circles, triangles), and under free diffusion (crosses, dashes). The solid black lines show the time range where the restricted diffusion effects dominate; the difference ∆M_SDR between these lines gives a contrast, over which signals can be coherently modulated by a suitable Selective Dynamical Decoupling (SDR) filter function.
Time evolution of the spin magnetization under CPMG (N = 8 pulses) and Hahn-echo sequences for spins diffusing in a restricted space (circles, triangles), and under free diffusion (crosses, dashes). The solid black lines show the time range where the restricted diffusion effects dominate; the difference ∆M_SDR between these lines gives a contrast, over which signals can be coherently modulated by a suitable Selective Dynamical Decoupling (SDR) filter function.
Experimental SDR signals normalized with the first data point (symbols) as a function of the x delays of the SDR sequence. The solid lines are analytical fittings of our model to the experimental curve. By using the measured diffusion coefficient D0 ∼ 2.3 × 10−5 cm^2/s, the fitted diameter d given in the plots is in agreement with the nominal value d = 5 ± 1μm.
Experimental SDR signals normalized with the first data point (symbols) as a function of the x delays of the SDR sequence. The solid lines are analytical fittings of our model to the experimental curve. By using the measured diffusion coefficient D0 ∼ 2.3 × 10−5 cm^2/s, the fitted diameter d given in the plots is in agreement with the nominal value d = 5 ± 1μm. The behavior of the SDR curves resemble the root mean square displacement of the diffusing spins in a restricted space: in both cases curves plateu for times x larger than the correlation time characteristic of achieving a restricted diffusion regime, evidence a full sampling of the restricting space.