As NV centers are surrounded by electrons, and electron spin is used as qubits but nuclear spin acts as a source of decoherence by creating a varying magnetic field. Now if the NV center is in quantum superposition state due to the decoherence the changes in energy levels will cause dephasing and eventually, the loss of quantum state. To counter this we apply an RF pulse to invert the state of NV center which inverts the effect of the magnetic field on the spin. This is justified by the fact that 'if we have the same time before and after this flip the effect of the field is canceled and quantum state is protected.' But how? And will the noise present in the system affect the protected quantum state? Can't these controlled spin be manipulated in a way so that they can act as qubits and help in carry extra information?
In spin systems in particular, commonly used protocols for dynamical decoupling include the Carr-Purcell and the Carr-Purcell-Meiboom-Gill schemes. They are based on the Hahn spin echo technique of applying periodic pulses to enable refocusing and hence extend the coherence times of qubits.
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