  Dynamic control of atomic dressing to the highly-excited Rydberg state in
multi-level systems has special appeals owing to the development of flexible
and precise measurement. In this study we develop an experimentally-accessible
proposal to robustly control the dressing probability via a three-step cascaded
excitation with double electromagnetically induced transparency (EIT)
technique. The system can function as an optical switch where the third
addressing laser serving as the control knob can switchably engineer the
dressing probability with time. Differing from a conventional two-photon EIT,
this novel scheme facilitates the maximal dressing probability determined by a
relative strength between two coupling fields, entirely relaxing the absolute
values for strong lasers. The collective feature caused by the interactions of
a few atoms is also studied leading to an enhanced dressing probability as well
as a reduced response time. Our work offers the opportunity to a coherent
dynamic control of Rydberg excitation and to realize sizable Rydberg-Rydberg
interactions in weakly-driven quantum systems.
