Ultrahigh- Q Torsional Nanomechanics through Bayesian Optimization

Recently, it was discovered that torsion modes of strained nanoribbons exhibit dissipation dilution, giving a route to enhanced torque sensing and quantum optomechanics experiments. As with all strained nanomechanical resonators, an important limitation is bending loss due to mode curvature at the clamps. Here we use Bayesian optimization to design nanoribbons with optimal dissipation dilution of the fundamental torsion mode. Applied to centimeter-scale Si3N4 nanoribbons, we realize Q factors exceeding 100 million and Q-frequency products exceeding 1013 Hz at room temperature. The thermal torque sensitivity of the reported devices is at the level of 10-20Nm/Hz, and the zero point angular displacement spectral density is at the level of 10-10rad/Hz; they are moreover simple to fabricate, have high thermal conductivity, and can be heavily mass-loaded without diminishing their Q, making them attractive for diverse fundamental and applied weak force sensing tasks.