Trace expressions and associated limits for nonequilibrium Casimir torque

Benjamin Strekha, Sean Molesky, Pengning Chao, Matthias Krüger, Alejandro W. Rodriguez

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We exploit fluctuational electrodynamics to present trace expressions for the torque experienced by arbitrary objects in a passive, nonabsorbing, rotationally invariant background environment. Specializing to a single object, this formalism, together with recently developed techniques for calculating bounds via Lagrange duality, is then used to derive limits on the maximum Casimir torque that a single object with an isotropic electric susceptibility can experience when out of equilibrium with its surrounding environment. The maximum torque achievable at any wavelength is shown to scale in proportion to body volumes in both subwavelength (quasistatics) and macroscopic (ray optics) settings, and come within an order of magnitude of achievable torques on topology optimized bodies. Finally, we discuss how to extend the formalism to multiple bodies, deriving expressions for the torque experienced by two subwavelength particles in proximity to one another.

Original languageEnglish (US)
Article number042222
JournalPhysical Review A
Issue number4
StatePublished - Oct 2022
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics


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