Quantum Decoherence of Nitrogen‐Vacancy Spin Ensembles in a Nitrogen Spin Bath in Diamond Under Dynamical Decoupling

ABSTRACT The negatively charged nitrogen‐vacancy (NV) center in diamond has emerged as a leading qubit platform. One of the key challenges for NV‐based quantum applications is building an accurate model to predict their decoherence properties. In this study, a combination of theory and experiment is used to investigate NV decoherence dynamics in the presence of P1 center baths. A cluster‐correlation expansion method to compute the decoherence under the Hahn‐echo and CPMG pulse sequences at various P1 concentrations from 1 to 300 ppm is employed. Notably, we find that the coherence time ( T 2 ) scales quadratically as a function of the pulse number, on a logarithmic scale, as opposed to the linear scaling predicted by widely accepted semi‐classical theories. In this experiment, the CPMG signal for two diamond samples with high P1 concentrations of 0.8 and 13 ppm is measured. It is demonstrated that the T 2 scaling is indeed quadratic, thus confirming our theoretical predictions. These results show that the quantum bath model combined with the CCE method can accurately capture the quantum nature of the P1‐driven NV decoherence. This study opens a new avenue for developing a complete noise model that can be used to optimize the performance of NV‐based quantum devices.