Characterizing the nitrogen-vacancy center singlet transition and its phonon sideband for absorption-based room-temperature magnetometry

Research Question and Approach

This study investigates the optical properties of the nitrogen-vacancy (NV) center's singlet transition at room temperature to improve the performance of absorption-based magnetometry. Conventional NV magnetometry typically relies on triplet fluorescence, which is limited by low photon collection efficiency and weak signal changes. The authors utilize a cavity-enhanced spectroscopy setup to measure the absorption of the NV- singlet transition and its associated phonon sideband across a broad spectral range (680-1050 nm). By employing microwave-induced signal changes, they isolate NV-specific effects from other defect-related optical signals, allowing for a precise quantification of the singlet absorption cross-section.

The researchers successfully mapped the room-temperature absorption spectrum of the NV- singlet transition. While the zero-phonon line (ZPL) at 1042 nm provides the highest contrast, the study identifies several additional peaks within the phonon sideband that offer significant contrast for magnetometry. By normalizing the cavity-enhanced data, the authors provide quasi-single-pass values for absorption and optically detected magnetic resonance (ODMR) contrast, with values reaching 50-80% in the singlet absorption regime. These results demonstrate that absorption-based magnetometry can achieve higher contrasts than traditional triplet-based fluorescence methods.

These findings provide a comprehensive characterization of the NV- singlet transition, which is critical for developing advanced magnetometers. By identifying multiple spectral regions with high ODMR contrast, the study relaxes the strict material requirements for probe lasers and gain media in laser threshold magnetometry (LTM). This work enables the design of more flexible and sensitive quantum sensors that can operate at room temperature, potentially overcoming the spectral limitations imposed by the 1042 nm ZPL and the performance constraints of silicon-based detectors.