Collective Dynamics of Atoms Coupled to an Optical Nanofiber: From Disordered Ensembles to Tunable Arrays

Abstract

Quantum emitters coupled to a nanophotonic waveguide have revolutionized quantum science and technology by enabling engineered light-matter interactions. In particular, a system of neutral atoms coupled to an optical nanofiber (ONF) offers a unique platform for quantum optics and quantum computation, as it integrates two well-established technologies: neutral atoms with high-fidelity control and optical fibers with low-loss light propagation. This thesis presents a study of the collective dynamics of Rb85 atoms coupled to an ONF, with a focus on the atomic spatial distribution.

We first present the collective dynamics of V-type multilevel quantum emitters, emphasizing the interaction between multiple excited states and multiple atoms mediated by a common electromagnetic (EM) field mode. Remarkably, we observe quantum beats even in the absence of an initial superposition in the excited states, which arises from vacuum-induced coupling between the excited levels. Although such second-order processes are typically weak, they can become observable through collective enhancement. We theoretically investigate these collective quantum beats in an extended system of V-type atoms coupled to a waveguide and identify a characteristic length scale that governs the interference in the multi-atom, multi-level emission.

Then, we describe our efforts to observe long-range interaction between macroscopically separated atomic clouds via an optical fiber. We develop a theoretical framework for modeling resonant scattering of an atomic ensemble placed in front of a mirror in the waveguide quantum electrodynamics (QED) setup. We identify the competition of two parameters that govern the scattering process: the drive strength and the strength of time-delayed feedback. Our intensity correlation measurement shows that an atomic cloud coupled to an ONF operates in the independent emission regime, where time-delayed feedback is negligible. This work highlights the need for an ordered atomic array with a lattice constant commensurate with the transition wavelength to collectively enhance cooperativity.

In the final chapter, we present a novel method for creating a tunable-spacing atomic array interfaced with an ONF using a set of binary phase transmission gratings. The optical setup and preliminary results on atom trapping within the lattice are described. Our approach opens the door to high-cooperativity neutral-atom-nanofiber interfaces, paving the way for advances in quantum optics and quantum technology.