EPR

Roshan Kumar (Indian Institute of Science Education and Research Bhopal, India)

Abstract: Advancing nanoscale quantum sensing requires robust control over internal nuclear spin baths and high-fidelity detection of external molecular targets. In this work, we characterized the coherent spin dynamics and magnetic sensing capabilities of shallow-implanted (≈ 10−15 nm) Nitrogen-Vacancy (NV) centers housed in waveguiding diamond nanopillars. We utilized optically detected magnetic resonance (ODMR), electron spin echo envelope modulation (ESEEM), and XY16 dynamical decoupling under varying static magnetic fields to probe both internal and external local spin environments.
Approaching the excited-state level anti-crossing (ESLAC) near 60 mT, we observed a contrast asymmetry between the 130 MHz C-13 hyperfine transitions, suggesting the onset of macroscopic C-13 dynamic nuclear polarization (DNP).
Additionally, we mapped the internal coupled spin dynamics, resolving the distinct Larmor and hyperfine modulation frequencies of the I = 1/2 N-15 nucleus and the nearby C-13 bath. To push the sensing volume beyond the diamond lattice, we applied the XY-16 dynamical decoupling protocol to filter nanotesla-scale AC magnetic fields generated by surface contamination layers. By measuring the fundamental and third-harmonic resonance intervals across two different bias B-fields, we detected decoherence features consistent with external proton spins on surface, yielding an extracted average gyromagnetic ratio of 41.7 − 42.0 MHz/T. These findings confirms that the nanopillar geometry helps mitigate the traditionally low signal-to-noise ratio of bulk single NV centers. Ultimately, this work highlights the potential of the shallow NV nanopillar platform as a sensitive and robust probe for future nanoscale external nuclear magnetic resonance (NMR) spectroscopy.