Wang successfully defends thesis, “Levitated Optomechanical Sensors for Fundamental Physics"

On July 28, Jiaxiang Wang successfully defended the thesis “Levitated Optomechanical Sensors for Fundamental Physics” (advisor: David Moore).

Wang explained, “Detecting weakly interacting particles such as dark‑matter candidates or neutrinos demands kinematic sensors with unprecedented sensitivity. Advances in optomechanical sensing over the past few decades have enabled precise control of mechanical oscillators, allowing the detection of extremely small displacements and forces. These developments shift the paradigm: rather than focusing on particle interactions at the atomic or subatomic scale within a detector, one can instead study how a particle perturbs the entire detector’s center-of-mass motion.”

Wang continued, “By optically trapping these systems in high vacuum, one can drastically reduce environmental noise and achieve exquisite control over the detector’s center-of-mass motion, rotational degrees of freedom, and physical characteristics such as charge states. With this level of isolation, the detector’s sensitivity can approach the measurement-limited background, making it a powerful platform for detecting small momentum transfers, such as those caused by ‘nugget’-like dark matter scattering. Furthermore, such levitated sensors can serve as novel probes of radioactive decay by implanting unstable isotopes directly into the detector and reconstructing the momentum of the decay products. This capability opens a new window into the study of forces underlying decay processes, offering exciting opportunities to explore the properties of neutrinos and other elusive particles.”

Thesis Abstract: Optomechanical detectors offer a highly sensitive method for measuring weak forces. By optically trapping these systems in high vacuum, one can drastically reduce environmental noise and achieve exquisite control over the detector’s center-of-mass motion, rotational degrees of freedom, and physical characteristics such as charge states. This level of isolation enables the detector’s noise to reach the quantum measurement regime, where the dominant noise source is the measurement process itself.

Such sensors are a powerful tool for detecting particle recoils, such as those from composite dark matter or other rare particle scattering events. These same detectors can also serve as probes for radioactive decays from isotopes directly implanted into the detector through momentum reconstruction of the decay products, which can enable the study of the forces imparted during radioactive decay processes. More broadly, mechanical particle detection opens exciting possibilities for studying neutral and weakly interacting particles, including neutrinos, thus providing a new platform for fundamental investigations in particle and nuclear physics.

I will describe the exquisite control we can apply to our levitated optomechanical sensor and its promising future as an impulse detector with the potential of working at the standard quantum limit. I will also describe our attempt to measure recoils from composite dark matter with long-range interactions and recent work to measure individual mechanical recoils from nuclear decays using an optically levitated optomechanical sensor.

Thesis committee: David Moore (advisor), Jack Harris, Konrad Lehnert, and Peter Rakich