• microwave coupling
• Autler-Townes splitting
• cold atoms
• Rydberg states
• facilitation

Rydberg atoms being in a well defined quantum state alongside their tunable long-range interactions, makes them an ideal system for conducting quantum computation, quantum simulation and quantum optics experiments. The typical interactions between the atoms are van der Waals interactions for the relevant interatomic distances in the cold rubidium atom samples in our experiments. A consequence of these interactions is facilitation where the energy of a Rydberg level gets shifted. When the interaction shift compensates for the detuning of the excitation laser from resonance, a facilitated excitation process can occur which aids off-resonant excitations into Rydberg states. The experimental studies reported in my thesis are mainly focused on detecting such facilitation processes by measuring the off-resonant excitations of S, D and P Rydberg states. Two types of facilitation experiments were performed, one was based on the interaction between the atoms in the same Rydberg state (S/D or P) while the other considered the interaction between atoms in two different Rydberg states (P-S or P-D ). The former is called intrastate facilitation and the latter is referred to as interstate facilitation. Microwaves were employed to excite atoms into two different Rydberg P states from the intermediate S/D state. The microwave Rabi frequency was measured experimentally from the Autler-Townes splitting between the two coupled Rydberg states. A qualitative analysis of Autler-Townes splitting in function of microwave polarization and power is also presented.
The reported experimental observations clearly show the intrastate facilitation on S and D states and interstate facilitation between P and S states. The intrastate facilitation signal observed on P states was weak and the possible reason behind it is discussed in this thesis.