Ilai Schwartz

Optically induced dynamic nuclear spin polarisation in diamond

The sensitivity of Magnetic Resonance Imaging (MRI) depends strongly on nuclear spin polarisation and, motivated by this observation, dynamical nuclear spin polarisation has recently been applied to enhance MRI protocols (Kurhanewicz, J., et al., Neoplasia 13, 81 (2011)). Nuclear spins associated with the 13 C carbon isotope (nuclear spin I = 1/2) in diamond possess uniquely long spin lattice relaxation times (Reynhardt, E.C. and G.L. High, Prog. in Nuc. Mag. Res. Sp. 38, 37 (2011)) If they are present in diamond nanocrystals, especially when strongly polarised, they form a promising contrast agent for MRI. Current schemes for achieving nuclear polarisation, however, require cryogenic temperatures. Here we demonstrate an efficient scheme that realises optically induced 13 C nuclear spin hyperpolarisation in diamond at room temperature and low ambient magnetic field. Optical pumping of a Nitrogen-Vacancy (NV) centre creates a continuously renewable electron spin polarisation which can be transferred to surrounding 13 C nuclear spins. Importantly for future applications we also realise polarisation protocols that are robust against an unknown misalignment between magnetic field and crystal axis.

Robust optical polarization of nuclear spin baths using Hamiltonian engineering of nitrogen-vacancy center quantum dynamics

A robust and fast principle of optical hyperpolarization is proposed and demonstrated by using NV centers experimentally. Dynamic nuclear polarization (DNP) is an important technique that uses polarization transfer from electron to nuclear spins to achieve nuclear hyperpolarization. Combining efficient DNP with optically polarized nitrogen-vacancy (NV) centers offers promising opportunities for novel technological applications, including nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarized nanodiamonds as magnetic resonance imaging contrast agents, and the initialization of nuclear spin–based diamond quantum simulators. However, none of the current realizations of polarization transfer are simultaneously robust and sufficiently efficient, making the realization of the applications extremely challenging. We introduce the concept of systematically designing polarization sequences by Hamiltonian engineering, resulting in polarization sequences that are robust and fast. We theoretically derive sequences and experimentally demonstrate that they are capable of efficient polarization transfer from optically polarized NV centers in diamond to the surrounding 13C nuclear spin bath even in the presence of control errors, making the abovementioned novel applications possible.Dynamical nuclear polarisation (DNP) is an important technique that uses polarisation transfer from electron to nuclear spins to achieve nuclear hyperpolarisation. As the electron spin of the nitrogen vacancy (NV) centres in diamond can be optically initialised nearly perfectly even at room temperature and ambient conditions, new opportunities become possible by the combination of efficient DNP with optically polarised NV centres. Among such applications are nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarised nanodiamonds as MRI contrast agents as well as the initialisation of nuclear spin based diamond quantum simulators. Current realisations of DNP perform the polarisation transfer by achieving energetic resonance between electrons and nuclei via carefully tuned microwave fields or by using quasi-adiabatic sweep-based schemes across resonance points. The former limits robustness against control errors while the latter limits polarisation rates, making the realisation of the applications extremely challenging. Here we introduce the concept of Hamiltonian engineering by pulse sequences and use it for the systematic design of polarisation sequences that are simultaneously robust and fast. We derive sequences theoretically and demonstrate experimentally that they are capable of efficient polarisation transfer from an optically polarised nitrogen-vacancy centre in diamond to the surrounding

Robust techniques for polarization and detection of nuclear spin ensembles

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Quantum control and sensing of nuclear spins by electron spins under power limitations.

C nuclear spin bath even in the presence of control errors, making it an ideal tool for the realisation of the above NV centre based applications.