Towards Quantum-Limited Spatial Resolution of NV-Diamond Magnetometry

PhoQus Group Members Prof. Guha and Students Declan Daly and Nico Deshler have published in the Journal Optica Publishing Group!

Professor Saikat Guha (lead of the Photonic Quantum Systems Group, PhoQuS, at the University of Maryland), UMD-affiliated researcher Nico Deshler, and UMD PhD student Declan Daly, together with collaborators Ayan Majumder and Kasturi Saha of the Indian Institute of Technology Bombay, have published “Quantum Limited Spatial Resolution of NV-Diamond Magnetometry” in Optica Quantum.

What the paper is about: The team tackles a longstanding challenge in solid-state quantum sensing: nitrogen vacancy (NV) centers in diamond are widely used for imaging-based magnetometry, thermometry, and strain sensing, but resolving individual defects within a tightly packed, sub-diffraction cluster has remained difficult, limiting access to atomic-scale features and dynamics.

To address this, the authors use optical spatial mode demultiplexing (SPADE) to improve localization and brightness-estimation accuracy at scales below the diffraction limit, developing a two-stage protocol that combines direct imaging with point-spread-function-adapted and Yuen-Kennedy-Lax (YKL) spatial mode measurements to efficiently recover emitter positions and brightnesses.

Key results: Compared with standard focal-plane intensity imaging, their SPADE-based protocol improves emitter localization accuracy by roughly 6x and brightness estimation accuracy by roughly 2x for tightly confined ensembles residing well below the diffraction limit. The team validated the approach on realistic sensing tasks, including continuous-wave optically detected magnetic resonance (ODMR) and Rabi oscillation experiments, showing substantial gains in recovering magnetic field and Rabi frequency estimates over conventional imaging.

Notably, the method is entirely passive — it requires no active modulation of the diamond sample or its environment, making it a promising, non-invasive route toward super-resolution sensing for applications in biology, chemistry, and quantum simulation where sample fragility is a concern.

Author roles: Deshler led the calculations and simulations; Daly contributed to developing the sensing modality; Majumder helped formulate the initial SPADE brightness-estimation approach; Guha and Saha jointly conceived the original concept and supervised the theoretical framework and its integration into NV magnetometry, respectively.

Authors: Nico Deshler, Declan Daly, Ayan Majumder, Kasturi Saha, and Saikat Guha.