Fiber Mirror Facility Upgrade for Quantum Optics and Sensing

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Optical cavities vastly enhance light-matter interactions, making them a ubiquitous tool in optics, quantum optics, and sensing. Recently, microscopic "fiber cavities" have emerged, offering significantly higher bandwidth and tighter confinement, thereby boosting these interactions even further. As a result, five of our six core research directions now rely on fiber cavity technology. The requisite fiber mirror substrates are laser-machined in a shared facility at McGill, and, while this system has vaulted our research to the leading edge of several fields, its low tolerances and lack of flexibility now threaten to halt further progress. As such, we request an upgrade that will improve precision, design flexibility, and throughput. Each research area will greatly benefit from this, but two recent breakthroughs in particular present extraordinary opportunities that prompt an immediate upgrade. First, in the field of optomechanics, we have successfully realized a system comprising an ultralow-noise "trampoline" micromechanical sensor within a fiber cavity, whose motion will be dominated by quantum radiation pressure fluctuations over an unprecedented band of frequencies. This quantum-dominated regime heralds the generation of "squeezed" light useful for surpassing the "standard quantum limit" and preparing arbitrary motional quantum states via feedback, enabling fundamental tests of quantum collapse (e.g. due to gravity), and quantum-enhanced sensors for dark matter searches and force microscopy. However, these exciting opportunities require significantly improved fiber mirrors to efficiently out-couple quantum light: we need precisely positioned, ultrasmooth, and near-flat surfaces that we cannot currently fabricate. Second, in the field of radiation dosimetry, we recently patented a tissue-equivalent in vivo fiber-cavity dosimeter with water as the active medium. Our collaboration with Prof. Enger (MUHC) has now observed promising signals in free space water, verified the radiation hardness of our mirror coatings, and developed techniques and a detailed theory for realizing the optimal dosimeter. We know that the targeted sensitivities require mirrors with much larger radius of curvature than is possible in our existing facility. The proposed upgrade -- which notably utilizes almost all of the existing infrastructure -- addresses all of the above issues, while increasing reliability and throughput. It includes motorized stages for multi-shot ablation of arbitrary profiles on multiple fiber tips and automatic profiling during and after ablation, a fiber cleaver with industry-leading angular tolerances to eliminate detrimental misalignment, and all necessary integration hardware. Beyond this, our facility provides fibers to researchers at Harvard, TU Denmark, Korea University, and Alberta. The infrastructure requested here will increase production, flexibility, and reliability, allowing this community to expand.