(color online) Protection of center spin coherence by dynamical decoupling (DD). (a) An NV electron spin (red) and its ¹³C nuclear spin bath (purple). The spin state of a strongly coupled ¹³C nuclear spin can be mapped to the electron spin through selective MW pulses. For weakly coupled nuclear spins, DD is employed to address one of them while decoupling the others. (b) Spin coherence as function of the total evolution time, while CPMG of different pulse numbers is applied. (c) Coherence of the center electron spin under CPMG-12 (red line) and CPMG-1 (gray line), as a function of the pulse interval τ. Different nuclear spins can be selectively addressed by choosing the value of τ. (d) Under the protection of a CPMG sequence, the NV spin state only accumulates a controllable phase from the selected target nuclear spin. Reproduced from Refs. [19] and [29], APS.