*Zoom* [PhD Thesis Presentation] ‐ Ms. Krishna Priya Subramonian Rajasree– “Multiphoton process in optical nanofiber-mediated cold Rydberg and ground state Rb atoms”

Optical nanofibers (ONF) offer tight confinement and diffraction-free propagation over a long distance. When the fiber is smaller than the wavelength of the propagating light, a large evanescent light field extends beyond the fiber surface. This evanescent field, when coupled to surrounding atoms, provides a unique platform for studies on atom-light interactions for fundamental understandings of atomic physics and applications for quantum technologies. My thesis will present experimental investigations performed using an ONF embedded in a cold 87Rb atomic ensemble. Neutral atoms in highly excited states, namely Rydberg states, exhibit exotic features such as a long lifetime and a huge dipole moment making them strongly interacting systems. Rydberg atoms near an ONF are an important candidate for fiber-based quantum networks and the physics of Rydberg atoms at subwavelength distances from dielectric surfaces is unexplored. In my PhD work, two-photon excitation is used to excite atoms to a Rydberg level via evanescent field coupling. Successful creation of the Rydberg atoms next to the ONF paves the way for further studies on the Rydberg atom-ONF system. Aside from work on the highly excited Rydberg atoms, we have also investigated single-colour two-photon excitation at 993 nm addressing the 5S1/2 to 6S1/2 transition in ground state atoms mediated via an ONF. Interesting effects arising from multi-levels interacting with multiple light fields at different intensity regimes are studied.