Casimir spring and dilution in macroscopic cavity optomechanics

• Published in: Nature physics Vol. 16; no. 11; pp. 1117 - 1122
• Main Authors: Pate, J. M., Goryachev, M., Chiao, R. Y., Sharping, J. E., Tobar, M. E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-11-2020; Nature Publishing Group
• Subjects: 639/766/1130/2800; 639/766/530/2803; Acoustics; Atomic; Boundary conditions; Cavity resonators; Classical and Continuum Physics; Coherence; Complex Systems; Condensed Matter Physics; Dilution; Energy dissipation; Gravitational waves; Mathematical and Computational Physics; Membranes; Molecular; Optical and Plasma Physics; Opto-mechanics; Phonons; Physics; Physics and Astronomy; Radiation; Room temperature; Stiffness; Theoretical; Zero point energy
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-020-0975-9

The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures, it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterize the effect at a range of temperatures and distances. In addition, in the rapidly evolving field of cavity optomechanics, there is an endeavour to manipulate phonons and enhance coherence. We demonstrate a way to realize a Casimir spring and engineer dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially localized Casimir spring mimics a non-contacting boundary condition, giving rise to increased strain and acoustic coherence through dissipation dilution. This provides a way to manipulate phonons via thermal photons leading to ‘in situ’ reconfigurable mechanical states, to reduce loss mechanisms and to create additional types of acoustic nonlinearity—all at room temperature.
An optomechanical cavity comprising a re-entrant cavity and membrane resonators can be tuned in and out of the Casimir regime. At the transition between the two regimes, the mechanical resonators exhibit a change in stiffness—the Casimir spring.