Non-conservative forces in optical tweezers and Brownian vortexes

Bo Sun, Alexander Y. Grosberg, David G. Grier

    Research output: Chapter in Book/Report/Conference proceedingConference contribution


    Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static, but non-conservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle's thermally-driven trajectory is not simply a deterministic response to the solenoidal component of the force, but rather reflects an interplay between advection and diffusion in which thermal fluctuations extract work from the non-conservative force field. As an example of this previously unrecognized class of stochastic machines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that non-conservative optical forces bias the particle's fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

    Original languageEnglish (US)
    Title of host publicationComplex Light and Optical Forces IV
    StatePublished - 2010
    EventComplex Light and Optical Forces IV - San Francisco, CA, United States
    Duration: Jan 27 2010Jan 28 2010

    Publication series

    NameProceedings of SPIE - The International Society for Optical Engineering
    ISSN (Print)0277-786X


    OtherComplex Light and Optical Forces IV
    Country/TerritoryUnited States
    CitySan Francisco, CA


    • Brownian vortex
    • Non-conservative force
    • Optical tweezers
    • Stochastic dynamics

    ASJC Scopus subject areas

    • Electronic, Optical and Magnetic Materials
    • Condensed Matter Physics
    • Computer Science Applications
    • Applied Mathematics
    • Electrical and Electronic Engineering


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