Microwave optomechanical measurement of non-metallized SiN strings at mK temperatures

TL;DR

This study introduces a dual-chip optomechanical method to measure non-metallized amorphous SiN strings at millikelvin temperatures, revealing low-temperature mechanical properties without metal-induced effects.

Contribution

It presents a novel dual-chip optomechanical technique for characterizing amorphous SiN strings at low temperatures, avoiding metal effects seen in traditional nanomechanical resonators.

Findings

Successful measurement of SiN string motion via microwave cavity

Characterization of low-temperature mechanical properties of non-metallized SiN

Demonstration of dielectric driving and detection of nanostrings

Abstract

The mechanical properties of amorphous materials (glasses) at low temperatures are dominated by effects of low energy excitations that are thought to be atomic-scale tunneling two level systems (TTLS). In nanometer-scale glass samples, the temperature dependence of the sound speed and dissipation is modified relative to that of bulk glass samples. In addition to this size effect, the usual presence of a polycrystalline metal in nanomechanical resonators leads to a further departure from the well-studied behavior of insulating bulk glass. We report a dual chip optomechanical measurement technique used to characterize non-metallized amorphous SiN strings at low temperatures. A harp consisting of SiN strings of width 350 nm and lengths 40 to 80 $\mu$m is coupled to an Al superconducting microwave cavity on a separate chip. The strings are driven dielectrically and their motion is detected via its modulation of the microwave resonance frequency.