Thermodynamic Geometry of Microscopic Heat Engines. (arXiv:1907.06780v1 [cond-mat.stat-mech])

We develop a geometric framework to describe the thermodynamics of
microscopic heat engines driven by slow periodic temperature variations and
modulations of a mechanical control parameter. Covering both the classical and
the quantum regime, our approach reveals a universal trade-off relation between
efficiency and power that follows solely from geometric arguments and holds for
any thermodynamically consistent microdynamics. Focusing on Lindblad dynamics,
we derive a second bound showing that coherence as a genuine quantum effect
inevitably reduces the performance of slow engine cycles regardless of the
driving amplitudes. To demonstrate the practical applicability of our results,
we work out the example of a single-qubit heat engine, which lies within the
range of current solid-state technologies.

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