Department of Physics Papers

Document Type

Journal Article

Date of this Version



We probe nonequilibrium properties of an active bacterial bath through measurements of correlations of passive tracer particles and the response function of a driven, optically trapped tracer. These measurements demonstrate violation of the fluctuation-dissipation theorem and enable us to extract the power spectrum of the active stress fluctuations. In some cases, we observe 1/√w scaling in the noise spectrum which we show can be derived from a theoretical model incorporating coupled stress, orientation, and concentration fluctuations of the bacteria.


Suggested Citation:
Chen, D.T.N., Lau, A.W.C., Hough, L.A., Islam, M.F., Goulian, M., Lubensky, T.C. and Yodh, A.G. (2007). Physical Review Letters. 99, 148302.

© 2007 The American Physical Society

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Physics Commons



Date Posted: 31 March 2011

This document has been peer reviewed.