An ultra-low-loss torsion balance leveraging nanoscale dissipation dilution*

Torsion balances play a key role in a diversity of pecision measurements. Recently there has been an effort to reduce their

dimensions to the micron scale, enabling chip-scale sensors and giving access to phenomena at the boundary of gravitational

and quantum physics. Here we describe a chip-scale torsion balance fashioned by suspending a rigid Si beam from a tensile-

strained Si3N4 nanoribbon. Stress in the nanoribbon produces a lossless torsion constant that dilutes the loss produced by

elastic deformation, yielding quality (Q) factors above 10^6 for the 10 Hz fundamental torsional mode of 0.1 mg prototype

devices, corresponding to an unprecedented (for this form factor) thermal torque sensitivity of 100 zNm/rt(Hz).  Inverting the

balance produces a resonance frequency shift of 10 Hz, pointing towards the possibility of a chip-scale micro-g gravimeter. Our

ultra-low-loss micromechanical torsion balance is easy to fabricate, lends itself to integration with on-chip light sources,

waveguides, patterned electrodes for detection and actuation schemes, and can be fabricated into arrays, hinting at a powerful

new platform for the quantum limited detection of forces below a piconewton.