We present a new class of ultra-low-loss torsion micropendula based on strain-engineered nanomechanics, and explore their application as parametric (clock) gravimeters. Specifically, by suspending a 0.1 mg Si paddle from a strained silicon nitride nanoribbon, we realize a 30 Hz torsion micropendulum with a damping rate of 20 micro-Hz, a parametric acceleration sensitivity of 6 Hz/g, and thermal acceleration noise of 3 ng/rtHz. By driving the pendulum into self-oscillation, we realize a clock gravimeter with a frequency stability as low as 50 parts-per-billion, corresponding to an acceleration resolution of 300 ng. Currently the limitation is the intrinsic nonlinearity of the pendulum, which transduces amplitude drift into frequency drift. We demonstrate how the duffing nonlinearity of the suspension can be used to cancel this nonlinearity, paving the way towards a fully isochronous, high-Q micromechanical clock.
Torsion resonators loom large in the history of precision measurement; however their role in modern nanomechanics experiments is limited. In this presentation I will describe a new class of ultra-high-Q torsion nanoresonators fashioned from strained nanoribbons, and how they might be used for imaging-based quantum optomechanics experiments and chip-scale intertial sensing. Specifically, using an optical lever, we have resolved the rotation of one such nanoribbon with an imprecision 100 times smaller than the zero-point motion of its fundamental torsion mode, paving the way towards observation of radiation pressure shot noise in torque. We have also found that a strained nanoribbon can be mass-loaded without changing its torsional Q. We have used this strategy to engineer a chip-scale torsion pendulum with an ultralow damping rate of 7 micro-hertz, sufficient to resolve micro-g fluctuations of the local gravitational field.
We present a new class of ultra-high-Q nanomechanical resonators based
on torsion modes of high-stress nanoribbons, and explore their
application for quantum optomechanics experiments and precision
optomechanical sensing. Specifically, we show that nanoribbons made of
high stress silicon nitride support torsion modes which are naturally
soft-clamped, yielding dissipation dilution factors as high as 10^4
and Q factors as high as 10^8 for the fundamental mode. We show that
these modes can be read out with optical lever measurements with an
imprecision below that at the standard quantum limit, paving the way
for a new branch of torsional quantum optomechanics. We also show
that nanoribbons can be mass-loaded without changing their torsional Q
factor. We use this strategy to engineer a chip-scale torsion balance
with an damping rate of 10 micro-hertz. We use this torsion balance
as a clock gravimeter to sence micro-g fluctuation in the local
gravitational field strength.
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