When
June 19, 2026, Noon – 3 p.m.
Where
Meinel 821
Title
An Ultralow-Loss Torsion Micropendulum for Chip-Scale Gravimetry
Abstract
Macroscopic torsion balances have long been central to precision gravitational measurements. This work explores a lithographically defined silicon nitride torsion micropendulum as a chip-scale torsion balance. The device consists of a silicon test mass suspended from a high-stress silicon nitride nanoribbon. Its unique hierarchy of gravitational, tensile, and elastic stiffnesses allows the device to retain a parametric gravity sensitivity near that of a canonical pendulum. In the primary device studied here, a 0.1 mg silicon paddle suspended from a 100 nm x 25 um x 7 mm silicon nitride nanoribbon exhibits a 32 Hz torsional resonance, a Q ~ 2e+6 corresponding to a damping rate of 16 uHz, a thermal acceleration sensitivity of 2e-9 g_0/rt(Hz), and a parametric gravity sensitivity of 5 Hz/g_0. Together, these properties form the platform for chip-scale gravimetry and for fundamental-physics experiments requiring low-loss micro- to milligram-scale mechanical oscillators.
We demonstrate this sensing platform in two complementary modes. In the frequency mode, the torsion micropendulum operates as a clock-like gravimeter whose resonance frequency shifts with orientation in Earth's gravitational field, reaching a bias stability of 5e-7 g_0 at 100 s. In displacement mode, the same device functions as a spring-mass accelerometer, enabling cross-spectral analysis with a concurrently monitored reference seismometer, forming a two-sensor network. Using this network, we observe the ocean-wave microseism from a laboratory in Tucson, demonstrating that the chip-scale device can resolve a real geophysical acceleration signal also seen by conventional seismic instrumentation. This dissertation also extends the silicon nitride torsion fiber suspension concept to related devices for short-range gravity, centimeter-scale lithographic torsion pendula, and macroscopic mass-loaded torsion balances aimed at tabletop tests of classical and quantum gravity. Together, the results establish mass-loaded silicon nitride torsion ribbons as a scalable platform for precision mechanical sensing across a wide range of masses, frequencies, and gravitational measurement geometries.
Please email Jini at jini@optics.arizona.edu or Charles at cacondos@arizona.edu for a Zoom link.