According to the laws of thermodynamics, no heat engine can beat the efficiency of a Carnot cycle. This efficiency traditionally comes with vanishing power output and practical designs, optimized for power, generally achieve far less. Recently, various strategies to obtain Carnot's efficiency at large power were proposed. However, a thermodynamic uncertainty relation implies that steady-state heat engines can operate in this regime only at the cost of large fluctuations that render them immensely unreliable. Here, we demonstrate that this unfortunate trade-off can be overcome by designs operating cyclically under quasistatic conditions. The experimentally relevant yet exactly solvable model of an overdamped Brownian heat engine is used to illustrate the formal result. Our study highlights that work in cyclic heat engines and that in quasistatic ones are different stochastic processes.

Charles University Faculty of Mathematics and Physics Department of Macromolecular Physics 5 Holešovičkách 2 CZ 180 00 Praha Czech Republic

Institut für Theoretische Physik Universität Leipzig Postfach 100 920 D 04009 Leipzig Germany

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Heat capacities of thermally manipulated mechanical oscillator at strong coupling