Universal and robust dynamic decoupling controls for zero-field magnetometry by using molecular clock sensors

Color centers in diamond and silicon carbide, and molecular spins through a host matrix control are promising for nanoscale quantum sensing because they can be optically addressable, coherently controllable, and placed proximate to the targets. However, large transverse zero-field splitting (ZFS) is often inevitable due to their intrinsic symmetry and/or the high local strains of the host matrix. Although spin coherence can be extended due to magnetic noise-insensitive clock transitions at a vanishing magnetic field, the eigenstates of these sensors are not sensitive to weak magnetic signals in the linear order. We address this challenge by employing a combination of radio-frequency (rf) field driving along the NV orientation and microwave dynamic decoupling pulse sequences. Radio-frequency driving can effectively mitigate the transverse ZFS effect and enhance the NV center's sensitivity to ac magnetic field signals. This combination not only suppresses environmental noise but also enables quantum frequency mixing between the transverse ZFS and the signal. It also offers the potential to detect weak ac signals at intermediate and high frequencies with high resolution, a task difficult to achieve using conventional methods.