Microwave coherent control of ultracold polar molecules with rotational-state double resonances

We report an experimental demonstration of microwave-assisted coherent control of ultracold $^{85}$Rb$^{133}$Cs molecules in a ladder-type configuration of rotational-state double resonances, following an observation of Rabi oscillations of the related neighbouring rotational states. The population of middle rotational states, which is coupled with a probe microwave (MW) field, can be reduced by a control MW field. Broadening of spectral splitting and shift of central frequency are observed and both are attributed to the control MW field. Applying Akaike's information criterion, we conclude that our observed coherent spectra happen near the crossover range of electromagnetically induced transparency and Aulter-Townes splitting. Our work is a significant development in microwave-assisted quantum control of ultracold polar molecules with multilevel configuration, and also offers a great potential in quantum information based on ultracold molecules.