Aluminum Nitride Photonic Integrated Circuits with Applications to Cold Atoms

Abstract

Quantum sensing has become foundational to many modern technologies. Precision time keeping is core to the global positioning system (GPS), magnetometry is core to mineral discovery for mining. The ability to measure with unparalleled sensitivity has driven many major technological improvements across diverse fields. From simple neutral atom vapour cells to sophisticated ion traps, atoms are a preeminent quantum sensing platform. However, these systems remain difficult to make field-deployable, owing largely to the complexity and fragility of their optical systems. As the invention of the laser and commercialization of external cavity diode lasers (ECDL) enabled increasingly complex trapped atom experiments this thesis aims to take a step toward the next stage: scalable, robust, and portable trapped-atom-based quantum sensors. I argue that a primary limitation to achieving this goal lies in the reliance on bulk optical systems, which exhibit poor size, weight, and power (SWaP) characteristics, are prone to misalignment, and require specialized assembly.

To overcome these limitations, I propose the use of photonic integrated circuits (PIC), leveraging fabrication tools and techniques from the semiconductor industry to create a versatile PIC "toolbox" for the trapped-atom community. The unique requirements of such systems motivate the choice of aluminum nitride (AlN) as the waveguiding material—a high-index, ultra-wide band gap, and electro-optically active medium that meets the optical and material needs of trapped-atom applications but has received relatively little attention compared to other established platforms. This thesis therefore details a reproducible nanofabrication process for AlN waveguides that achieves state-of-the-art propagation losses through the use of atomic layer deposition and rapid thermal annealing. Rather than treating this process as proprietary, the complete recipe is shared here for the benefit of the broader AlN research community. I also present the first demonstration of a hybrid ECDL incorporating an AlN photonic integrated circuit, an important milestone toward realizing fully integrated on-chip light sources. These hybrid ECDL operate near 852 nm and 650 nm, addressing optical transitions in cesium and barium ions. Finally, I describe a novel dual-mode phase shifter that combines electro-optic and thermo-optic tuning within a single fabrication layer, enabling both high-speed modulation and large index changes. Collectively, the work presented in this thesis represents a significant step toward fully integrated, chip-scale optical systems for trapped-atom experiments—paving the way for the next generation of compact, deployable quantum sensors.