Shift-driven modulations of spin-echo signals | Proc. Natl. Acad. Sci. U. S. A. 109, 5958 (2012).

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Pieter E. S. Smith, Guy Bensky, Gonzalo A. Álvarez, Gershon Kurizki, and Lucio Frydman

Abstract:

Since the pioneering works of Carr-Purcell and Meiboom-Gill [Carr HY, Purcell EM (1954) Phys Rev 94:630; Meiboom S, Gill D (1985) Rev Sci Instrum 29:688], trains of π-pulses have featured amongst the main tools of quantum control. Echo trains find widespread use in nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI), thanks to their ability to free the evolution of a spin-1/2 from several sources of decoherence. Spin echoes have also been researched in dynamic decoupling scenarios, for prolonging the lifetimes of quantum states or coherences. Inspired by this search we introduce a family of spin-echo sequences, which can still detect site-specific interactions like the chemical shift. This is achieved thanks to the presence of weak environmental fluctuations of common occurrence in high-field NMR—such as homonuclear spin-spin couplings or chemical/biochemical exchanges. Both intuitive and rigorous derivations of the resulting “selective dynamical recoupling” sequences are provided. Applications of these novel experiments are given for a variety of NMR scenarios including determinations of shift effects under inhomogeneities overwhelming individual chemical identities, and model-free characterizations of chemically exchanging partners.chemical exchange dynamic decoupling magnetic field inhomogeneity magnetic resonance quantum control

via Proc. Natl. Acad. Sci. U. S. A. 109, 5958 (2012): Shift-driven modulations of spin-echo signals.

Behavior observed for the illustrated compound (Cynnamic acid) upon implementing the proposed selective dynamical recoupling (SDR) sequence, as mediated by homonuclear 1H-1H couplings, for the indicated parameters. Experiments (black traces) are compared against simulations (red) using the indicated parameters, and analytical curves (blue) arise from the two-site modulation predicted by our results. (A) x-dependence observed for the isolated olefinic proton pair of Cynnamic acid at high-resolution. (B) Idem but for the Cynnamic acid placed in a grossly inhomogeneous magnetic field (shimming coils off), illustrating SDR’s ability to retrieve high resolution shift modulations. While it relies on fully refocused π-pulse trains that normally cancel also the shift modulations, by the assistance of slowly fluctuations due to the homonuclear 1H-1H couplings the shift modulation are selectively reintroduced.
Behavior observed for the illustrated compound (Cynnamic acid) upon implementing the proposed selective dynamical recoupling (SDR) sequence, as mediated by homonuclear 1H-1H couplings, for the indicated parameters. Experiments (black traces) are compared against simulations (red) using the indicated parameters, and analytical curves (blue) arise from the two-site modulation predicted by our results. (A) x-dependence observed for the isolated olefinic proton pair of Cynnamic acid at high-resolution. (B) Idem but for the Cynnamic acid placed in a grossly inhomogeneous magnetic field (shimming coils off), illustrating SDR’s ability to retrieve high resolution shift modulations. While it relies on fully refocused π-pulse trains that normally cancel also the shift modulations, by the assistance of slowly fluctuations due to the homonuclear 1H-1H couplings the shift modulation are selectively reintroduced.

Copyright ©2012 by the National Academy of Sciences

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3 thoughts on “Shift-driven modulations of spin-echo signals | Proc. Natl. Acad. Sci. U. S. A. 109, 5958 (2012).

    […] modulations that can serve for example to probe chemical identities derived from chemical shifts [2]. Alternatively, SDR can be designed to selectively measure the correlation time of the […]

    […] modulations that can serve for example to probe chemical identities derived from chemical shifts [2]. Alternatively, SDR can be designed to selectively measure the correlation time of the […]

    […] 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, 5…], allows one to coherently reintroduce diffusion decoherence effects driven by fluctuations arising […]

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