Massive dissipation dilution of a nanomechanical torsion resonator*

Strained nanomechanical resonators have been shown to exhibit ultrahigh quality

factors due to dissipation dilution. While the mechanism of dissipation dilution has been

extensively studied for transverse flexural modes of nanobeams and membranes, it is

commonly held that it does not apply to torsion modes. Here we show that torsion

modes can experience massive dissipation dilution due to tensile stress and draw a

connection to a century-old theory from the torsion balance community that suggests

that a torsion beam is naturally soft-clamped. Enabling this advance is the fabrication of

high-stress Si₃ N₄ nanobeams with width-to-thickness ratios of 10⁴ and the discovery that

their torsion modes have Q factors that scale as the width-to-thickness ratio squared,

yielding Q factors as high as 10⁸ and Q-frequency products as high as 10¹³ Hz. By

disrupting a commonly held belief in the nanomechanics community, our findings invite

a rethinking of strategies towards quantum experiments and precision measurement

with nanomechanical resonators.