Noise-Limited Sensitivity in Cavity Optomechanical Molecular Sensing Enabled by Quantum Zero-Point Displacement Coupling and Strong Photon-Phonon Interaction for Chiral Detection

Abstract: This work presents a quantum-limited optomechanical sensing platform for real-time detection and discrimination of chiral molecules, based on a multilayer hybrid plasmonic-mechanical resonator. Leveraging quantum zero-point motion and engineered photon-phonon interactions, the system achieves ultrahigh displacement sensitivity that approaches the fundamental quantum limit. The multilayer architecture, composed of alternating dielectric and metallic films, supports mechanical resonances with quality factors reaching approximately ten thousand in the megahertz frequency range. These resonances coherently modulate the optical field through radiation pressure and dynamical backaction. Power spectral density measurements reveal distinct mechanical peaks at 0.68, 2.9, 4.3, 5.5, and 6.8 MHz, with optomechanical coupling strengths exceeding twice the intrinsic baseline, enabling highly efficient signal transduction. Lorentzian fitting confirms the presence of sharp mechanical linewidths, while the total force noise, including thermal, shot, and technical contributions, remains below the threshold required for detecting sub-piconewton forces. Time-resolved Raman spectroscopy, which is typically insensitive to chirality, here reveals enantioselective dynamics arising from asymmetric optomechanical interactions, enabling clear spectral distinction between d- and l-enantiomers. Finite-element simulations validate the strong spatial overlap between optical confinement and mechanical displacement modes. This platform offers a scalable and tunable approach to quantum-limited, high-sensitivity chiral molecule detection, with applications in coherent control, precision spectroscopy, and chemical sensing.