Novel Parametric Processes For Quantum Information Processing Using Rubidium Vapor Based Photonic Platforms

Abstract

Large Kerr nonlinearities are of significant interest for photonic quantum information processing and can be applied towards developing deterministic single photon sources and implementing deterministic quantum logic gates. The required strong nonlinear interaction between photons can be achieved by enhancing the light-matter interaction using alkali vapors interacting with a tightly confined optical mode area, such as that of a waveguide. The guiding properties of the waveguide over long distances helps in achieving a long interaction length while simultaneously increasing the atom-photon coupling by maintaining a small mode area over the entire guiding length. In this thesis, we explore the large effective Kerr nonlinearities (γ) of Rubidium vapor interacting with the optical mode of hollow-core photonic band-gap fibers (Rb-PBGF) and the tightly confined evanescent field of air-clad silicon nitride waveguides (Rb-chip). We have demonstrated efficient and noiseless frequency conversion at low power levels leveraging the large γ for the Rb-PBGF system. As proof of principle, we have also generated spectrally bright quantum correlated photon-pairs in a warm Rb vapor-cell and have proposed an extension of the experiment in the Rb-PBGF platform, which could lead to near unit photon pair generation efficiency. During the course of the study, we have also significantly improved the Rb-PBGF system by attaining an almost continuous operation lasting for several hours (1000X longer) while generating optical depths (OD's) ~ 50, which are required to attain single photon-level nonlinearity in the Rb-PBGF system. Developing on-chip CMOS [complimentary metal-oxide-semiconductor] compatible Rb vapor based platforms can not only achieve large γ, but also significantly reduce the footprint of the device and make it more compatible with other chip-based platforms. In our present work, we have demonstrated the feasibility of this approach by achieving extended interaction time-scales for, air-clad silicon nitride waveguides coated with aluminum oxide and evanescently coupled to warm Rb vapor. The thin aluminum oxide layer has greatly helped in preventing corrosive damage caused by Rb to the nitride surface that have improved the operational lifetimes by a factor > 100. During the course of our study, we realized the limitations of known platforms towards generating tunable sources of single photons at near-visible wavelengths; a wavelength regime at which great progress has been made for quantum storage and detection. Towards the end of this work, we have experimentally demonstrated a broadband frequency comb at near-visible wavelengths by engineering anomalous dispersion for higher order waveguide modes in silicon nitride microresonators. The underling process of parametric wave-mixing being the same for frequency combs and correlated photon-pair generation; our work opens new possibilities for developing spectrally narrow single photon sources in the near-visible which are compatible with highly nonlinear alkali vapor based systems like the Rb-PBGF and Rb-chip platform.