Creating and probing laser-cooled atomic ensembles inside a hollow-core optical fibre

Abstract

A laser-cooled atomic ensemble confined inside a hollow-core optical fiber offers a unique platform for enhanced light-matter interactions and their applications. At the same time, transferring a cloud of laser-cooled atoms from a free space magneto-optical trap into the few-micron diameter core of the optical fiber presents a host of experimental challenges (and requires optimization of in a multidimensional parameter space). This thesis investigates loading of laser-cooled caesium atoms into a hollow-core photonic-crystal fiber, develops diagnostic methods to optimize the process and probe the atoms inside the fiber, presents initial experiments exploring the optical properties of the fiber-confined atomic ensemble, and discusses the potential uses of fiber-confined atomic ensembles in ’hybrid’ quantum repeaters that utilize quantum dots as source of entangled photon pairs. Fluorescence-based methods are also employed to estimate atom numbers and assess temperature of the atomic cloud collected initially in the magneto-optical trap and to aid in the alignment of the atom cloud with the fiber’s core. Machine learning, specifically Gaussian processes, is explored as a means to optimize experimental parameters. M-LOOP, a Python-based tool, is utilized for this purpose, demonstrating its ability to navigate around local minima. The influence of dipole beam characteristics, such as intensity and resonance, on loading efficiency is examined, considering factors like Stark shifts and trap depth. The dissertation also delves into two-photon electromagnetically induced absorption (TPEIA) with cold atomic cesium, highlighting the importance of optical depth for efficient wavelength conversion. The ladder scheme is discussed, showcasing its potential for quantum memory systems with modest delays in electromagnetically induced transparency (EIT) media. The concept of slow light under EIT conditions is presented, illustrating its utility in optical communication traffic buffering and quantum memory. We also discuss the potential uses of this platform in a quantum repeater.