Diamond nanomechanics at cryogenic temperature reveals two-level-system dynamics and topological dissipation

Mechanical resonators form the basis of today's most sensitive measurements, from gravitational-wave detectors to atomic-scale force sensors. Yet progressing their ultimate precision has long been impeded by challenges in understanding material loss dynamics. Here, we utilize a van der Waals-strained diamond nanomechanical platform that operates at cryogenic temperature with quality factors approaching 10 billion to study the intrinsic loss origins. By sweeping temperature over four decades, we identify two distinct dissipation channels governed by two-level systems: localized surface-bond rotors and a distributed ensemble arising from lattice disorder. Surprisingly, an unexpected topological dissipation channel emerges in the dilution temperature that originates from the monolayer superfluid film at the resonator surface. These results establish strain‑engineered diamond nanomechanics as both an ultrasensitive strain sensor and a new probe of low-temperature quantum matter, bridging precision metrology and condensed matter physics.