  The atom-light interaction in a three-level system has shown significant
physical phenomena, such as electromagnetically induced transparency and
Autler{Townes splitting (ATS), for broad applications in classical and quantum
information techniques. Here, we optimally demonstrated the ATS with a quantum
state manipulation method. The ATS in the dephasing-dominated diamond NV center
system was successfully recovered by coherent microwave control, which cannot
be observed with traditional method. The dynamical process of ATS was
investigated in detail, revealing a nontrivial quantum interference with
geometric phase modulations. Based on the quantum interference, the signal of
the optimal ATS is twice as intense as those with traditional observation
method.
