Zero- and Low-Field Sensing with Nitrogen-Vacancy Centers

Over the years, an enormous effort has been made to establish nitrogen vacancy (N -V) centers in dia-mond as easily accessible and precise magnetic field sensors. However, most of their sensing protocols rely on the application of bias magnetic fields, preventing their usage in zero-or low-field experiments. We overcome this limitation by exploiting the full spin S = 1 nature of the N -V center, allowing us to detect nuclear spin signals at zero and low field with a linearly polarized microwave field. As conventional dynamical decoupling protocols fail in this regime, we develop robust pulse sequences and optimize pulse pairs, which allow us to sense temperature and weak ac magnetic fields and achieve an efficient decoupling from environmental noise. Our work allows for much broader and simpler applications of N -V centers as magnetic field sensors in the zero-and low-field regime and can be further extended to three-level systems in ions and atoms.