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Optical Polarization of Nuclear Ensembles in Diamond


  R. Fischer [1]  ,  C. Bretschneider [2]  ,  P. London [1]  ,  D. Budker [3,4]  ,  D. Gershoni [1]  ,  L. Frydman [2]  
 [1] Physics Department, Technion-Israel Institute of Technology, Israel
[2] Chemical Physics, Weizmann Institute, Israel
[3] Department of Physics, UC Berkeley
[4] Nuclear Science Division, LBNL, Berkeley

Nuclear spins are a natural choice for applications requiring long relaxation times due to their immunity to unwanted perturbations from the environment. Among the many applications are magnetic resonance-based bio-sensing, rotation sensing, and quantum computing. However, thermal polarization of nuclear spins, determined by the Boltzmann factor, is particularly low, especially at room temperature. This limitation results in poor sensitivities, requiring methods that achieve an enhancement over thermal polarization. To overcome this limitation, numerous theoretical and experimental studies have been carried out demonstrating a transfer of electron-spin polarization to the nuclei – a field of study known as dynamic nuclear polarization ‎[1]. However, these polarization methods are applicable at cryogenic temperatures, while ambient temperature hyperpolarization is mostly beyond reach.

We report strongly enhanced bulk 13C polarization in diamond at room-temperature. The polarization method is based on the transfer of electron spin polarization of negatively charged nitrogen-vacancy color centers to the nuclear spins via the excited-state level anti-crossing of the center. We demonstrate a 13C bulk nuclear polarization of ~0.5% - equivalent to polarization achieved by thermal means at fields of ~2000 T ‎‎[2]. Additionally, we show control over the polarization sign by tuning the axial magnetic field magnitude.

Owing to its simplicity, this 13C room-temperature polarizing strategy provides a promising new addition to existing nuclear hyper-polarization techniques, which is of interest in applications of nuclear magnetic resonance, in quantum memories of hybrid quantum devices, and in sensing.

[1] J. H. Ardenkjær-Larsen, B. Fridlund, A. Gram, G. Hansson, M. H. Lerche, R. Servin, M. Thaning, and K. Golman,Proc. Natl. Acad. Sci. U.S.A.100, 10 158 (2003).

[2] R. Fischer, C. Bretschneider, P. London, D. Budker, D. Gershoni, L. Frydman, "Bulk Nuclear Polarization Enhanced at Room-Temperature by Optical Pumping", Phys. Rev. Lett. 111, 057601 (2013).