A broad effort is underway to improve the sensitivity of nuclear magnetic resonance through the use of dynamic nuclear polarization. Nitrogen-vacancy (NV) centers in diamond offer an appealing platform because these paramagnetic defects can be optically polarized efficiently at room temperature. However, work thus far has been mainly limited to single crystals because most polarization transfer protocols are sensitive to misalignment between the NV and magnetic field axes. Here we study the spin dynamics of NV-¹³C pairs in the simultaneous presence of optical excitation and microwave frequency sweeps at low magnetic fields. We show that a subtle interplay between illumination intensity, frequency sweep rate, and hyperfine coupling strength leads to efficient, sweep-direction-dependent ¹³C spin polarization over a broad range of orientations of the magnetic field. In particular, our results strongly suggest that finely-tuned, moderately coupled nuclear spins are key to the hyperpolarization process, which makes this mechanism distinct from other known dynamic polarization channels. These findings pave the route to applications where powders are intrinsically advantageous, including the hyper-polarization of target fluids in contact with the diamond surface or the use of hyperpolarized particles as contrast agents for in-vivo imaging.

Dr. Maria Belen Franzoni joins us from Cordoba, Argentina for a month-long stay in our group. Belen is an experimentalist with expertise in the physics and applications of solid-state magnetic resonance. She will be working with us on the use of NV centers in diamond for nuclear spin hyperpolarization. We are delighted to have you here, Belen!

The press release of our Optica article can be found here. A Phys.Org article can be seen here.

Applications of quantum science to computing, cryptography, and imaging are on their way to becoming key next- generation technologies. Owing to the high-speed transmission and exceptional noise properties of photons, quantum photonic architectures are likely to play a central role. A long-standing hurdle, however, has been the realization of robust, device-compatible single-photon sources that can be activated and controlled on demand. Here we demon- strate large arrays of room-temperature quantum emitters in two-dimensional hexagonal boron nitride (hBN). The large energy gap inherent to this van der Waals material stabilizes the emitters at room temperature within nanoscale regions defined by substrate-induced deformation of few-atomic-layer hBN. Through the control of pillar geometry, we demonstrate an average of ∼2 emitters per site for the smallest pillars (75 nm diameter). These findings set the stage for realizing arrays of room-temperature single-photon sources through the combined control of strain and external electrostatic potentials.

From the abstract in Jake’s thesis:

“In this dissertation, experiments surrounding the charge state dynamics and the carrier dynamics are performed and analyzed. Extensive studies of the ionization and recombination processes of defects in diamond, specifically, the Nitrogen Vacancy (NV) center, have been performed. Diffusion of ionized charge carriers has been imaged indirectly through the recapture of said carriers by optically active defects such as the NV center and the Silicon Vacancy (SiV) center. With proper understanding of the carrier dynamics, diamond stands to be a strong competitor in the field of spintronics for quantum information processing. Additionally, the understanding of these charge state dynamics is utilized in a novel proof of principle experiment, showing that the NV center defect’s charge state could serve as an ultra- dense 3D memory platform.”

The ability to optically polarize the spin of NV centers in diamond under ambient conditions has long been considered a valuable resource for nuclear spin hyperpolarization and MRI. Unfortunately, the misalignment between the external magnetic field and the NV axis inherent to a powder – the preferred geometry in the above applications – has proven an obstacle difficult to surmount. The work by Ajoy et al. demonstrates efficient 13C polarization in a diamond powder under ambient conditions and in the presence of mild optical and MW excitation, thus paving the route to portable, affordable hyperpolarization platforms of widespread applicability. Click here to gain access to the full Science Advances article.

Dwi is a PhD student woking under the supervision of Prof. Toshu An at the Japan Advanced Institute of Science and Technology (JAIST). His main research interests are diamond NV magnetometry and spin-heat interaction in ferromagnetic materials. He received an Off-campus Research Travel Grant from JAIST for his three-month stay at the Meriles Group. Welcome, Dwi!

Alex is a physicist now working as a postdoc at the group of Prof. Andrew Martin at the University of Melbourne. With a formal training in experimental atomic physics, his work has been more recently broadened to include the dynamics of NV and SiV centers in diamond. He is particularly interested in the interplay between the NV spin and the physical rotation of the host crystal. He will be working with us for about a month and a half. We are really glad to have him here!