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

This work demonstrates a quantum-limited optomechanical sensing platform for real-time detection and discrimination of chiral molecules, based on a multilayer hybrid plasmonic–mechanical resonator. By exploiting quantum zero-point motion and engineered photon–phonon interactions, the system achieves a displacement sensitivity on the order of 10⁻¹⁷\,m/√Hz, approaching the standard quantum limit. The engineered multilayer stack, composed of alternating dielectric and metallic layers, supports high-Q mechanical resonances (Q factors up to ~10,000) in the MHz regime, which coherently modulate the multilayer optical field via radiation pressure and dynamical backaction. Power spectral density measurements exhibit distinct mechanical peaks at 0.68, 2.9, 4.3, 5.5, and 6.8\,MHz, with single-photon coupling rates up to 2.6 times the intrinsic baseline, enabling strong optomechanical transduction. Lorentzian fitting confirms narrow mechanical linewidths, while the total noise floor—including thermal, shot, and technical contributions—remains below 10⁻¹⁶\,N/√Hz, ensuring robust detection of sub-piconewton forces. Time-resolved Raman spectroscopy, typically insensitive to chirality, here reveals enantioselective dynamics due to asymmetric optomechanical coupling in the hybrid cavity, enabling clear spectral differentiation of {d}- and {l}-enantiomers. Finite-element simulations corroborate the strong spatial overlap between optical confinement and mechanical displacement fields. This study establishes a scalable and tunable platform for high-sensitivity, quantum-limited detection of chiral molecules, with potential applications in coherent control, precision molecular spectroscopy, and ultrasensitive chemical sensing.