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1. Towards imaging-based quantum optomechanics

   https://doi.org/10.1117/12.3001998  

   Pluchar, Christian M; He, Wenhua; Choi, Morgan; Manley, Jack; Deshler, Nico; Guha, Saikat; Wilson, Dalziel J (March 2024, SPIE)

   Shahriar, Selim M; Scheuer, Jacob (Ed.)

   Quantum optomechanics has led to advances in quantum sensing, optical manipulation of mechanical systems, and macroscopic quantum physics. However, previous studies have typically focused on dispersive optomechanical coupling, which modifies the phase of the light field. Here, we discuss recent advances in “imaging-based” quantum optomechanics – where information about the mechanical resonator’s motion is imprinted onto the spatial mode of the optical field, akin to how information encoded in an image. Additionally, we find radiation pressure backaction, a phenomenon not usually discussed in imaging studies, comes from spatially uncorrelated fluctuations of the optical field. First, we examine a simple thought experiment in which the displacement of a membrane resonator can be measured by extracting the amplitude of specific spatial modes. Torsion modes are naturally measured with this coupling and are interesting for applications such as precision torque sensing, tests of gravity, and measurements of angular displacement at and beyond the standard quantum limit. As an experimental demonstration, we measure the angular displacement of the torsion mode of a Si3N4 nanoribbon near the quantum imprecision limit using both an optical lever and a spatial mode demultiplexer. Finally, we discuss the potential for future imaging-based quantum optomechanics experiments, including observing pondermotive squeezing of different spatial modes and quantum back-action evasion in angular displacement measurements. 

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2. Quantum-limited imaging of a nanomechanical resonator with a spatial mode sorter

   https://doi.org/10.1103/6msj-wh2f  

   Choi, M E; Pluchar, C M; He, W; Guha, S; Wilson, D J (August 2025, Physical Review Research)

   We explore the use of a spatial mode sorter to image a nanomechanical resonator, with the goal of studying the quantum limits of active imaging and extending the toolbox for optomechanical force sensing. In our experiment, we reflect a Gaussian laser beam from a vibrating nanoribbon and pass the reflected beam through a commercial spatial mode demultiplexer (Cailabs Proteus). The intensity in each demultiplexed channel depends on the mechanical modeshapes and encodes information about their displacement amplitudes. As a concrete demonstration, we monitor the angular displacement of the ribbon’s fundamental torsion mode by illuminating in the fundamental Hermite-Gauss mode ( ${\mathrm{HG}}_{00}$) and reading out in the ${\mathrm{HG}}_{10}$mode. We show that this technique permits readout of the ribbon’s torsional vibration with a precision near the quantum limit. Our results highlight new opportunities at the interface of quantum imaging and quantum optomechanics. 

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3. Coherent optical coupling to surface acoustic wave devices

   https://doi.org/10.1038/s41467-024-48167-7  

   Iyer, Arjun; Kandel, Yadav P.; Xu, Wendao; Nichol, John M.; Renninger, William H. (May 2024, Nature Communications)

   Abstract Surface acoustic waves (SAW) and associated devices are ideal for sensing, metrology, and hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to Gaussian surface acoustic wave cavities with small mode volumes and high quality factors (>10⁵measured here) through a Brillouin-like optomechanical interaction. High-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates are efficiently optically accessed along piezo-active directions, as well as non-piezo-active (electromechanically inaccessible) directions. The precise optical technique uniquely enables controlled analysis of dissipation mechanisms as well as detailed transverse spatial mode spectroscopy. These advantages combined with simple fabrication, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems. 

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4. Quantum-limited optical lever measurement of a torsion oscillator

   https://doi.org/10.1364/OPTICA.549814  

   Pluchar, C_M; Agrawal, A_R; Wilson, D_J (March 2025, Optica)

   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 exceptionally high torque sensitivity or, equivalently, zero-point angular displacement spectral density. Here, we describe optical lever measurements on nanoribbons possessing torsion modes with torque sensitivities of and zero-point displacement spectral densities of . By compensating for 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 Si₃N₄phonons. Our study signals the potential for a new class of torsional quantum optomechanics. 

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5. Optomechanical crystal with bound states in the continuum

   https://doi.org/10.1038/s41467-022-30965-6  

   Liu, Shengyan; Tong, Hao; Fang, Kejie (June 2022, Nature Communications)

   Abstract Chipscale micro- and nano-optomechanical systems, hinging on the intangible radiation-pressure force, have shown their unique strength in sensing, signal transduction, and exploration of quantum physics with mechanical resonators. Optomechanical crystals, as one of the leading device platforms, enable simultaneous molding of the band structure of optical photons and microwave phonons with strong optomechanical coupling. Here, we demonstrate a new breed of optomechanical crystals in two-dimensional slab-on-substrate structures empowered by mechanical bound states in the continuum (BICs) at 8 GHz. We show symmetry-induced BIC emergence with optomechanical couplings up tog/2π≈ 2.5 MHz per unit cell, on par with low-dimensional optomechanical crystals. Our work paves the way towards exploration of photon-phonon interaction beyond suspended microcavities, which might lead to new applications of optomechanics from phonon sensing to quantum transduction. 

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