Quantum Fluctuation Theorems for arbitrary environments

Sept. 10, 2018

Thermodynamics, the branch of physics concerned with heat and temperature and their relation to energy and work, can be extended far beyond the large macroscopic systems of our daily lives.  However, stochastic fluctuations in thermodynamic quantities—like work, heat, and entropy—become essential to the thermodynamics of small systems. Nevertheless, these fluctuations turn out to be more than random noise: their statistics are imprinted by the time-reversal symmetry of the underlying dynamics, satisfying a class of universal relations called “fluctuation theorems”. Fluctuation theorems have been developed for small quantum systems, mostly focusing on systems coupled with ideal thermal equilibrium environments.

An international team of researchers from the Massachusetts Institute of Technology (USA), the Universidad Complutense de Madrid (Spain), and the Institute of Interdisciplinary Physics and Complex Systems (IFISC, UIB-CSIC), has published a study in Physical Review X in which they focused on lifting this assumption of equilibrium environments because of the effective finite size of realistic thermal baths and the possibility of engineering non-thermal reservoirs with quantum properties. These generalized environments provide new sources of free energy and may pave the way for heat engines surpassing traditional limits on performance. In this study, they demonstrate the existence of fluctuation theorems for a variety of classical and quantum environments, and they show that in some situations the total entropy can be decomposed into two different contributions: the adiabatic and non-adiabatic (without/with transfer exchange of heat in the system) entropy productions, accounting for different sources of irreversibility.

These results may have profound implications for studies of small quantum devices performing thermodynamic tasks, such as extracting work or refrigerating, and may help to clarify the role of “quantumness” in thermodynamics.


Gonzalo Manzano, Jordan M. Horowitz, and Juan M. R. Parrondo. Phys. Rev. X 8, 031037. DOI: https://doi.org/10.1103/PhysRevX.8.031037


 Quantum Fluctuation Theorems



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