Extended Data Fig. 1: Suitable tip position for T2 enhancement in ‘pushing’ step.
From: Coherence enhancement of solid-state qubits by local manipulation of the electron spin bath
a, The confocal mapping when a negatively biased tip is scanned over a single shallow NV centre. The dark disk-like feature corresponds to NV+ state, caused by the strong tip-induced upward band bending effect. Scale bar: 500 nm. Laser power: 30 μW. Tip bias: −220 V. b, Schematic diagram showing the tip-induced band bending effect. When the tip is laterally close to NV within 300 nm, the large upward band bending effect induced by the negatively biased tip leads to NV+ state. The charge transition levels of NV+/NV0 and NV0/NVˉ are denoted by the short blue and red lines, respectively. The charge transition level of paramagnetic spins is denoted by the purple line. EF is the Fermi level, EC and EV denote the edges of the conduction and valance bands, respectively. c,d, Spin-echo mapping of one NV centre in the ‘pushing’ step under the tip bias of −100 V and −150 V, respectively, by fixing the delay time of spin-echo measurements. The images were expanded from 20 × 20 pixels to 40 × 40 pixels through the interpolation. The white disc denotes the position of NV. A grey arrow denotes the scanning direction, along which an overall decay of spin-echo signal was observed due to the thermal drift during the 6-hours imaging. The ‘hot’ regions demonstrating the longer T2 time are highlighted by the dashed curves. Scale bar: 400 nm. e, The T2 measurements at different positions in c. At every position denoted by the alphabets in c, we applied spin-echo measurements at full time range and fitted the T2. The dashed horizontal line denotes the original T2. The variation of T2 in e indicates the suitable tip position for enhancing the T2 under the ‘pushing’ step.
