Date of Award

Fall 1-1-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering (ENAS)

First Advisor

Tang, Hong

Abstract

Quantum information science, offering unprecedented potential compared to classical technologies, has undergone vast growth over the past decades. The proposed quantum computers promise the ability to solve complex problems that are practically intractable for classical computers; long range quantum networks are also envisioned as secure links to distribute both quantum and classical information. The demand to build these large-scale and sophisticated quantum architectures promotes the necessity of hybrid quantum systems, in which different platforms are pursued and interfaced according to specific needs. Among them, the solid state spins have drawn great attention for applications such as spin qubits, single photon source, quantum repeaters, and transducers. The rare earth ion (REI) further stands out as a promising candidate for these purposes due to its narrow and highly coherent optical and spin transitions. Lithium niobate, on the other hand, has served as a widely used host material for REIs. More importantly, it is one of the most fundamental building blocks in modern photonics, thanks to its unparalleled nonlinear, electro-optic, and piezoelectric properties. By incorporating REIs into the recent advanced thin-film lithium niobate integrated photonic platform, the advantages of both systems can be fused to realize high-performance and multi-functional quantum devices. In this thesis, we present the development of quantum photonic devices by incorporating erbium (Er) ions into lithium niobate thin films. We start with establishing material platforms to couple two systems, followed by device development for different quantum applications. Heterogeneous integration of Er doped bulk crystal and lithium niobate waveguides is first pursued and characterized with a plasma-assisted direct bonding method. Based on this approach, device design toward efficient microwave-to-optical transducers is proposed and tested. In view of the limitation in heterogeneous coupling, we proceed to study the direct doping of Er into thin-film lithium niobate. Two methods including post ion implantation and smart-cut technique are studied. The latter, which guarantees undiminished coherent properties compared to bulk crystals, is chosen for next-step investigation. On this platform, we demonstrate the control of single ion emission in an electro-optic photonic crystal nanobeam cavity. Coherence toward radiative limit is also achieved. Both results serve as necessary prerequisites for realizing spin qubits and coherent single photon sources. We further utilize the mechanical properties of lithium niobate to develop Er doped piezo-optomechanical Fabry-Perot cavities. We show that the Er fluorescence process can be used as filters in the phonon counting process, which is an important aspect in examining macroscopic quantum effects. The discussion also extends to future optimization and expansion of device structures from these results, as pathways to a broader spectrum of quantum applications.

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