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arXiv · 2409.11397

Quantum-limited optical lever measurement of a torsion oscillator

Christian M. Pluchar·Aman R. Agrawal·Dalziel J. Wilson
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Abstract

The optical lever is a precision displacement sensor with broad applications. In principle, it can track the motion of a mechanical oscillator with added noise at the Standard Quantum Limit (SQL); however, demonstrating this performance requires an oscillator with an exceptionally high torque sensitivity, or, equivalently, zero-point angular displacement spectral density. Here, we describe optical lever measurements on Si$_3$N$_4$ nanoribbons possessing $Q>3\times 10^7$ torsion modes with torque sensitivities of $10^{-20}\,\text{N m}/\sqrt{\text{Hz}}$ and zero-point displacement spectral densities of $10^{-10}\,\text{rad}/\sqrt{\text{Hz}}$. Compensating aberrations and leveraging immunity to classical intensity noise, we realize angular displacement measurements with imprecisions 20 dB below the SQL and demonstrate feedback cooling, using a position modulated laser beam as a torque actuator, from room temperature to $\sim5000$ phonons. Our study signals the potential for a new class of torsional quantum optomechanics.

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Christian M. Pluchar, Aman R. Agrawal, Dalziel J. Wilson. 2024-09-17. Quantum-limited optical lever measurement of a torsion oscillator. https://doi.org/10.1364/optica.549814

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