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A micrometre-sized heat engine operating between bacterial reservoirs

Nature Physics volume 12, pages 11341138 (2016) | Download Citation

Abstract

Artificial microscale heat engines are prototypical models to explore the mechanisms of energy transduction in a fluctuation-dominated regime1,2. The heat engines realized so far on this scale have operated between thermal reservoirs, such that stochastic thermodynamics provides a precise framework for quantifying their performance3,4,5,6. It remains to be seen whether these concepts readily carry over to situations where the reservoirs are out of equilibrium7, a scenario of particular importance to the functioning of synthetic8,9 and biological10 microscale engines and motors. Here, we experimentally realize a micrometre-sized active Stirling engine by periodically cycling a colloidal particle in a time-varying optical potential across bacterial baths characterized by different degrees of activity. We find that the displacement statistics of the trapped particle becomes increasingly non-Gaussian with activity and contributes substantially to the overall power output and the efficiency. Remarkably, even for engines with the same energy input, differences in non-Gaussianity of reservoir noise results in distinct performances. At high activities, the efficiency of our engines surpasses the equilibrium saturation limit of Stirling efficiency, the maximum efficiency of a Stirling engine where the ratio of cold to hot reservoir temperatures is vanishingly small. Our experiments provide fundamental insights into the functioning of micromotors and engines operating out of equilibrium.

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Acknowledgements

We thank U. Seifert for illuminating discussions and S. Ramaswamy and S. Gokhale for critical comments on our manuscript. S.K. thanks the J C Bose Fellowship of the Department of Science and Technology (DST) for fellowship support. S.G. thanks the Council of Scientific and Industrial Research for fellowship support. D.C. thanks the Department of Biotechnology for financial support. A.K.S. thanks the J C Bose Fellowship of the DST, India for support. R.G. thanks the ICMS and SSL, JNCASR for financial support.

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Affiliations

  1. Department of Physics, Indian Institute of Science, Bangalore - 560012, India

    • Sudeesh Krishnamurthy
    •  & A. K. Sood
  2. Molecular Biophysics Unit, Indian Institute of Science, Bangalore - 560012, India

    • Subho Ghosh
    •  & Dipankar Chatterji
  3. International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore - 560064, India

    • Rajesh Ganapathy
    •  & A. K. Sood
  4. Sheikh Saqr Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore - 560064, India

    • Rajesh Ganapathy

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Contributions

S.K., R.G. and A.K.S. conceived the project. S.K. designed and performed the experiments. S.G. and D.C. contributed towards handling and complete characterization of the bacteria. S.K., R.G. and A.K.S. analysed results. S.K., R.G. and A.K.S. wrote the paper with inputs from D.C. and S.G.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to A. K. Sood.

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https://doi.org/10.1038/nphys3870

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