Extended Data Fig. 4: Sensitivity enhancement for proton detection.
From: Coherence enhancement of solid-state qubits by local manipulation of the electron spin bath
a, Schematics showing the principle of detecting external protons by single NV centre. An ensemble of protons within the detecting volume (highlighted) contribute signals. b, The calculated sensitivity of single NV and its dependence on nτ according to the Equation 5. The detected field strength \(B_{{{{\mathrm{rms}}}}}^2\) is chosen to be fitted from the red curve in d. The grey curve shows the corresponding signal contrast calculated by the Equation 4. The blue curve shows the sensitivity calculated based on the approximation of tiny signal contrast (Supplementary Text 5). Only within the region of small signal contrast (highlighted), the red and blue curve show good consistence. For simplicity, both the sensitivity and signal contrast were calculated by setting \(C(n\tau )\)=1. c, Spin-echo measurements of a very shallow NV showing T2 enhancement of ~20 fold with our method. d, XY8-2 (blue curve) and XY8-12 (red curve) measurements of the same NV in c showing that after ‘pull-and-push’ method, such a quantum sensor with poor coherence can be used for detecting external protons, with the capability of detecting a minimum magnetic variance corresponding to ~0.18 protons. The red curve is offset for clarity. The external magnetic field is 303 Gauss.
