Characterization of Color centers in diamond for quantum sensing

Nitrogen-Vacancy (NV) centers in diamond are versatile quantum systems that combine single-photon emission with spin-dependent fluorescence. These properties have established NVs as a leading platform in the fields of quantum communication, computation, and sensing. Their spin-dependent optical readout enables nanoscale magnetic field detection. Moreover, the exceptional chemical stability and biocompatibility of diamond make NVs suitable for applications ranging from condensed matter to biology.

In this work, NV centers created in bulk diamond and nanodiamonds using different creation methods were characterized to investigate how fabrication conditions affect their optical and spin properties. Confocal and hyperspectral microscopy, emission spectroscopy, fluorescence lifetime imaging microscopy and optically detected magnetic resonance experiments were employed to probe the NV centers.

A comparative analysis was conducted between NVs created by ion implantation, high-temperature electron irradiation, and femtosecond laser writing. The ion-implanted bulk diamond presented well-defined quantum signatures with a dephasing time T2* = 118 ± 19 ns. Nanodiamonds with NV centers exhibited stable fluorescence, although with broader resonances indicating reduced magnetic sensitivity.

In contrast, NV ensembles generated by femtosecond laser writing demonstrated tunable photoluminescence, strongly dependent on laser writing parameters such as pulse energy, exposure time, and writing depth. The NV spots, located about 50 μm deep, show a long dephasing time, T2* = 0.32 ± 0.12 μs. These findings offer valuable insight into the optimization of NV-based quantum sensors by emphasizing that the fabrication method, which determines the NV centers’ depth and local environment, directly impacts their spin and optical properties.