(National Institute for Theoretical Physics (NITheP), Stellenbosch, South Africa)
We analyze the temporal evolution of the population of ultracold polar molecules in a microwave (mw) field with circular polarization. The molecules are in their ground 1Σ state and treated as rigid rotors with permanent dipole moments which interact with each other via the dipole-dipole (DD) interaction VDD. The mw field mixes states with different quantum and photon numbers, creating a field-dressed basis. Previous studies show that molecular collisional dynamics is mostly controlled by the ratios of mw field frequency vs rotational constant, and mw field Rabi frequency vs rotational constant. There exists a special scattering process which is elastic by nature and due to rotational energy exchange between the ground and first excited rotational states. We solve Schrödinger’s equation for the bare and dressed states under different mw field parameters and molecular gas characteristics. Depending on the ratio of mw field Rabi frequency and magnitude of the rotational exchange DD interaction, beating and oscillations occur in the populations of bare and dressed states. At a certain relation between mw detuning δ and DD interaction δ = ±VDD, two peak structures appear in the population of the excited bare states, which resembles the phenomenon of antiblockade. Each peak is associated with an avoided crossing between the dressed states adiabatic curves at the same position of mw detuning.