We present a new method for high-resolution nanoscale magnetic resonance imaging (nano-MRI) that combines the high spin sensitivity of nanowire-based magnetic resonance detection with high-spectral-resolution nuclear magnetic resonance (NMR) spectroscopy. Using a new method that incorporates average Hamiltonian theory into optimal control pulse engineering, we demonstrate NMR pulses that achieve high-fidelity quantum control of nuclear spins in nanometer-scale ensembles. We apply this capability to perform dynamical decoupling experiments that achieve a factor of 500 reduction of the proton-spin resonance linewidth in a (50−nm)3 volume of polystyrene. We make use of the enhanced spin coherence times to perform Fourier-transform imaging of proton spins with a one-dimensional slice thickness below 2 nm.Received 20 July 2017Revised 10 January 2018DOI:https://doi.org/10.1103/PhysRevX.8.011030Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCompositionQuantum controlPhysical SystemsNanowiresTechniquesMagnetic resonance imagingNuclear magnetic resonanceCondensed Matter, Materials & Applied Physics
Extensions of average Hamiltonian theory to quantum computation permit the design of arbitrary Hamiltonians, allowing rotations throughout a large Hilbert space. In this way, the kinematics and dynamics of any quantum system may be simulated by a quantum computer. A basis mapping between the systems dictates the average Hamiltonian in the quantum computer needed to implement the desired Hamiltonian in the simulated system. The flexibility of the procedure is illustrated with NMR on ${}^{13}\mathrm{C}$ labeled alanine by creating the nonphysical Hamiltonian ${\ensuremath{\sigma}}_{z}{\ensuremath{\sigma}}_{z}{\ensuremath{\sigma}}_{z}$ corresponding to a three-body interaction.
We develop a linear response formalism for nuclear spin diffusion in a dipolar coupled solid. The theory applies to the high-temperature, long-wavelength regime studied in the recent experiments of Boutis et al. [Phys. Rev. Lett. 92, 137201 (2004)], which provided direct measurement of interspin energy diffusion in such a system. A systematic expansion of Kubo's formula in the flip-flop term of the Hamiltonian is used to calculate the diffusion coefficients. We show that this approach is equivalent to the method of Lowe and Gade [Phys. Rev. 156, 817 (1967)] and Kaplan [Phys. Rev. B 2, 4578 (1970)], but has several calculational and conceptual advantages. Although the lowest orders in this expansion agree with the experimental results for magnetization diffusion, this is not the case for energy diffusion. Possible reasons for this disparity are suggested.
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Here we report the application of two-dimensional NMR double quantum filtered correlation spectroscopy to characterize the interactions between components in biphasic, heterogeneous media. The method was applied to model systems of carbon black reinforced rubber. The presence of filler particles induces local susceptibility fields while a local partial ordering of the elastomer at the surface prevents the complete averaging of the dipolar interaction. The separation of susceptibility and dipolar interactions allows for the direct observation of three elastomer components near the surface of filler particles: (1) encapsulated, (2) ordered surface layer, and (3) unordered layer near the surface. The NMR method permits one to quantify the amounts of elastomer in each of these regions and to estimate the thickness of the surface component. The method is applied to study several rubber samples for which the carbon black particle size distributions were determined from scanning electron microscopy measurements. For these samples the length scale of the surface elastomer component is estimated, and it is shown that the encapsulated elastomer is most probably located between the graphitic plates of the filler particles rather than in the space between adjacent particles.
Underlying disorder in skyrmion materials may both inhibit and facilitate skyrmion reorientations and changes in topology. The identification of these disorder-induced topologically active regimes is critical to realizing robust skyrmion spintronic implementations, yet few studies exist for disordered bulk samples. Here, we employ small-angle neutron scattering (SANS) and micromagnetic simulations to examine the influence of skyrmion order on skyrmion lattice formation, transition, and reorientation dynamics across the phase space of a disordered polycrystalline ${\mathrm{Co}}_{8}{\mathrm{Zn}}_{8}{\mathrm{Mn}}_{4}$ bulk sample. Our measurements reveal a disordered-to-ordered skyrmion square lattice transition pathway characterized by the promotion of fourfold order in SANS and accompanied by a change in topology of the system, reinforced through micromagnetic simulations. Pinning responses are observed to dominate skyrmion dynamics in the metastable triangular lattice phase, enhancing skyrmion stabilization through a remarkable skyrmion memory effect which reproduces previous ordering processes and persists in zero field. These results uncover the cooperative interplay of anisotropy and disorder in skyrmion formation and restructuring dynamics, establishing tunable pathways for skyrmion manipulation.
Neutron interferometry has played a distinctive role in fundamental science and characterization of materials. Moir\'e neutron interferometers are candidate next-generation instruments: they offer microscopy-like magnification of the signal, enabling direct camera recording of interference patterns across the full neutron wavelength spectrum. Here we demonstrate the extension of phase-grating moir\'e interferometry to two-dimensional geometries. Our fork-dislocation phase gratings reveal phase singularities in the moir\'e pattern, and we explore orthogonal moir\'e patterns with two-dimensional phase-gratings. Our measurements of phase topologies and gravitationally induced phase shifts are in good agreement with theory. These techniques can be implemented in existing neutron instruments to advance interferometric analyses of emerging materials and precision measurements of fundamental constants.
