Department of Physics Papers

Document Type

Journal Article

Date of this Version



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


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.


Date Posted: 31 March 2011

This document has been peer reviewed.