Extended Data Fig. 5: Laser power dependence of surface polarization.
From: Coherence enhancement of solid-state qubits by local manipulation of the electron spin bath
The fluorescence of one shallow NV centre under varied laser power with tip bias of +50 V (red points). The NVˉ completely coverts into NV+ at ~100 μW, which can be considered as a criterion for the degree of surface polarization. Assuming that there is no geometric change in the gaussian-like focus spot at different laser power, this transition laser power can be used for the estimation of polarized area. For example, considering the typical size of our laser focus and the power used during the ‘pulling’ step, we can estimate a polarized area of ~ 265 × 265 nm2 under a laser power of ~300 μW and a tip bias of +50 V. Inset: the schematics showing the process of surface polarization described in Methods. When polarizing the surface, we fixed the laser focus on one NV centre and scanned the tip with positive bias around it.
