Programmable Photonic Waveguide Array Quantum Processors
Quantum computers leverage quantum mechanics to process information, promising solutions to problems that remain intractable for even the most advanced classical supercomputers. Although various physical platforms have been explored for quantum computation, encoding quantum information in single photons stands out due to its inherent resistance to decoherence and the ability to manipulate photons with high fidelity through linear optical networks. In addition to programmable photonic circuits for quantum state manipulation, single-photon sources, and detectors are crucial for quantum state preparation and readout. Integrated photonic circuits, supported by the rapid advancements in semiconductor technology, offer a powerful avenue for miniaturizing and scaling optical quantum processors.
Waveguide arrays (WAs) represent a unique platform in integrated photonics, enabling ``always-on'' Hamiltonians that provide direct access to higher-dimensional quantum systems. However, conventional WAs have largely been application-specific and fixed in functionality. In contrast, programmable waveguide arrays (PWAs) introduce dynamic reconfigurability by leveraging electro-optic materials, such as lithium niobate, enabled by micrometer-scale tuners placed between waveguides. PWAs not only overcome the limitations of application-specific WAs and traditional MZI-based architectures, such as the need for bends to route light paths and their sensitivity to fabrication imperfections, but also hold promise for significantly enhancing the scalability and versatility of photonic quantum processors.
This thesis addresses significant research gaps by investigating the photonic device design, simulation, and experimental demonstration of PWAs as quantum processors. Previous work has not adequately explored how precise, reconfigurable control can be integrated into platforms that leverage electro-optic effects. By focusing on challenges in WAs and MZI-based architectures, this work fills a critical void in our understanding of how to design, simulate, characterize, and control PWAs, and how they can reliably enhance the scalability and versatility of photonic systems. The thesis begins with an overview of quantum information theory and the manipulation of photons as carriers of quantum information. It then introduces the fundamentals of integrated quantum photonics and PWAs, followed by two key experimental demonstrations on an 11-dimensional PWA based on lithium niobate (LN, LiNbO3) and a novel design for a tunable directional coupler. Finally, the work reviews the evolution of waveguide arrays and programmable waveguide arrays, proposing a vision for integrating PWAs into advanced photonic circuits and highlighting their transformative potential across interdisciplinary applications.
