All posts by cmeriles_1ry5wvws

03-19: Pablo’s paper on proxy-spin-mediated dynamic nuclear polarization published in Nano Letters as ASAP article.

Optically-pumped color centers in semiconductor powders can potentially induce high levels of nuclear spin polarization in surrounding solids or fluids at or near ambient conditions, but complications stemming from the random orientation of the particles and the presence of unpolarized paramagnetic defects hinder the flow of polarization beyond the defect’s host material. Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy (NV) and substitutional nitrogen (P1) centers in diamond to show that outside protons spin-polarize efficiently upon a magnetic field sweep across the NV–P1 level anti-crossing. The process can be interpreted in terms of an NV–P1 spin ratchet, whose handedness —and hence the sign of the resulting nuclear polarization — depends on the relative timing of the optical excitation pulse. Further, we find that the polarization transfer mechanism is robust to NV misalignment relative to the external magnetic field, and efficient over a broad range of electron-electron and electron-nuclear spin couplings, even if proxy spins feature short coherence or spin-lattice relaxation times. Therefore, these results pave the route towards the dynamic nuclear polarization of arbitrary spin targets brought in proximity with a diamond powder under ambient conditions.

12-18: Pablo’s paper on diamond-based DNP accepted in PNAS. Congratulations to Pablo and all co-authors!

13C spin polarization as a function of the relative magnetic field orientation

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.

10-18: We welcome our visitor, Dr. Belen Franzoni, from Universidad Nacional de Cordoba, Argentina. Good to have you here, Belen!

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!

09-18: Nick’s paper on activated photon emitters in a 2D host published in Optica. Congratulations, Nick!

Atomic force microscopy image of an hBN thin film on a patterned substrate. In the imaged region, part of the film folds on itself (2L region). Upon optical excitation, light is selectively emitted from the pillar sites due to local activation of color centers through strain-induced charge trapping.

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.