This dissertation consists of three microwave spectroscopy experiments performed with cold Rb Rydberg atoms in Magneto Optical Trap. The first experiment is a systematic study of a particular type of transition which was first observed in 2012 that involves a pair of Rydberg atoms. In this transition, even though only one microwave photon is absorbed, both atoms in the pair change states. In particular, we describe the transition with the configuration interaction (CI) model and experimentally

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... erify the scaling of fractional population transfer predicted by the CI model. The second experiment builds on the first experiment and reports observations of additional single and multi photon microwave transitions that are allowed due to the same CI as in the first experiment. The observations show clearly that this type of transition involving a pair of Rydberg atoms are a lot more common than initially thought. We show that the transitions can be conveniently described as Forster resonances of Floquet states. The last experiment reports on the technique we used to measure the ng and nh series quantum defects and the ionic dipole and quadrupole polarizabilities of 85 Rb. The technique allows us to obtain zero field intervals of (n + 1)d 5/2 → ng and (n + 1)d 5/2 → nh intervals despite the fact that we can only control the stray electric field in one direction. Using the technique, the quantum defects of ng and nh were determined to be 0.0039741(16) and 0.0014066(57), respectively. The ionic II dipole and quadrupole polarizabilities were determined to be 9.12(2)a 3 0 and 14(3)a 5 0 , respectively. III Acknowledgement As I approach the end of my career as a graduate student, I realize how fortunate I have been in every corner of my life. I have come across many great people to whom