Magnetics Business & Technology - Fall 2013 - (Page 22)

RESEARCH & DEVELOPMENT Researchers Increase NMR/MRI Sensitivity Through Hyperpolarization of Nuclei in Diamond Today’s nuclear magnetic resonance (NMR) and Magnetic Res- quantum information processing, and nuclear spintronics. onance Imaging (MRI) technologies, like quantum information “The nearly complete polarization of the spin of carbon-13 nuprocessing and nuclear spintronic technologies, are based on an clei is ideal for any process that requires a pure initial spin state,” intrinsic quantum property of electrons said Bajaj, who also holds an appointand atomic nuclei called “spin.” Electrons ment with the University of California and nuclei can act like tiny bar magnets (UC) Berkeley as a project scientist for with a spin that is assigned a directional the California Institute for Quantitative state of either “up” or “down.” NMR/ Biosciences (QB3). “More importantly, MRI signals depend upon a majority of our method should be applicable in any nuclear spins being polarized to point in situation where hyperpolarized bulk one direction. The greater the polarizaatomic nuclei are required, including tion, the stronger the signal. Researchdynamic nuclear polarization-enhanced ers with the US Department of Energy NMR and spintronic devices.” (DOE)’s Lawrence Berkeley National Over several decades Pines and memLaboratory (Berkeley Lab) have reported bers of his research group have develon a technique for hyperpolarizing caroped numerous ways to hyperpolarize bon-13 nuclear spins in diamond that the spins of atomic nuclei. Their efforts enhances the sensitivity of NMR/MRI have yielded NMR/MRI signals that are by many orders of magnitude above what 10,000 times stronger than those seen in is ordinarily possible with conventional conventional NMR/MRI experiments. In Hyperpolarizing carbon-13 nuclear spins in diamond NMR magnets at room temperature. several applications, they have also been holds implications for enhancing NMR/MRI sensitiv Hyperpolarizing carbon-13 nuclear ity in applications related to molecular and biomolecu- able to record analytically detailed magspins in diamond holds implications lar detection, diamond-based quantum information netic resonance spectra in the absence of for enhancing NMR/MRI sensitivity in processing, and nuclear spintronics. any magnetic field. In this latest effort, applications related to molecular and Pines and Bajaj capitalized on a diamond biomolecular detection, diamond-based impurity called a nitrogen-vacancy (NV) quantum information processing, and center, in which optical and spin degrees nuclear spin-based spintronics. Hyof freedom are coupled. perpolarizing carbon-13 nuclear spins The crystal of a pure diamond is a threein diamond holds implications for endimensional lattice of carbon atoms, each hancing NMR/MRI sensitivity in apof which is bonded to four of its neighplications related to molecular and bors. An NV center is created when two biomolecular detection, diamond-based adjacent carbon atoms are removed from quantum information processing and the lattice leaving two gaps, one of which nuclear spintronics. is filled with a nitrogen atom, and one of As part of a collaboration between the which remains vacant. This leaves unresearch groups of Alexander Pines and bound electrons in the center between the Dmitry Budker of Berkeley Lab’s Manitrogen atom and the vacancy that give terials Sciences Division, Vikram Bajaj rise to unique and well-defined electron led the demonstration of the first nearly spin polarization states. complete, magnetically controlled hy The Berkeley Lab researchers used perpolarization of the spins of carbon-13 Atomic representation of an NV center in a diamond a low-strength magnetic field to transwhich nitrogen atom fills one missing nuclei located near synthetic defects in lattice in and thea other missing carbon site is leftcar- fer NV center electron spin polarization bon site vadiamond crystals. The work builds upon cant. The nuclear spin of the nearby carbon-13 atom to nearby carbon-13 nuclei, resulting in earlier research by several groups world- has been hyperpolarized. hyperpolarized nuclei. This spin transferwide including those of Budker and ence process, which is called “dynamic Berkeley Lab’s Jeffrey Reimer. This spin hyperpolarization can nuclear polarization,” is routinely used to enhance NMR signals, be carried out with refrigerator-style magnets, resulting in pre- but has always required high-strength magnetic fields, cryogenic dictable and robust control of carbon-13 hyperpolarization. The temperatures and microwave irradiation. The Berkeley Lab remethodology suggests a route by which the sensitivity of generic searchers eliminated these requirements simply by placing a perNMR and MRI experiments can be enhanced in applications re- manent magnet near the diamond. lated to molecular and biomolecular detection, diamond-based “For efficient spin transfer, the energy structure of the source and 22 Magnetics Business & Technology • Fall 2013 www.MagneticsMagazine.com http://www.MagneticsMagazine.com

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Magnetics Business & Technology - Fall 2013