Concatenated continuous dynamical decoupling of ensemble NV centers in diamond for GHz- range AC magnetometry

Sensitive magnetometry using negatively-charged nitrogen-vacancy(NV) centers has been demonstrated with a large number of controlled spins, where the inhomogeneity of the bias magnetic field and control field play an important role in sensitivity. Several techniques are known to be robust against such inhomogeneity, including pulsed dynamical decoupling, shaped pulses, and so on. However, it is not trivial to apply them to GHz-range AC magnetometry based on Rabi oscillations. Alternatively, concatenated continuous dynamical decoupling(CCDD) is known to be robust for this purpose, but most of these studies have been limited to a small number of spins. In this presentation, we experimentally demonstrate GHz-range AC magnetometry with a large number of NV centers by use of CCDD. By comparing its performance to the direct Rabi method, we show that the robustness of the dressed states by CCDD enables the sensing of weaker GHz-range AC magnetic field.