Anomalous heat flow and quantum Otto cycle with indefinite causal order

TL;DR

This paper demonstrates that indefinite causal order in quantum systems can cause heat to flow from cold to hot, enabling novel thermodynamic cycles like refrigeration and work generation, confirmed through photonic experiments.

Contribution

It introduces the concept of anomalous heat flow due to indefinite causal order and designs a quantum Otto cycle utilizing this phenomenon, with experimental validation.

Findings

Anomalous heat flow from cold to hot observed.

Quantum Otto cycle achieves refrigeration and work.

Experimental photonic setup confirms theoretical predictions.

Abstract

The principle that heat spontaneously flows from higher temperature to lower temperature is a cornerstone of classical thermodynamics, often assumed to be independent of the sequence of interactions. While this holds true for macroscopic systems at equilibrium, here we show that, when the order of interactions between two identical thermalization channels is indefinite, an anomalous heat flow emerges, whereby heat can sometime flow from a colder entity to a hotter one. Taking advantage of this anomalous heat flow, we design a quantum Otto cycle with indefinite causal order, which not only achieves refrigeration but also generates work. The anomalous heat flow and the quantum Otto cycle are experimentally simulated in a photonic quantum setup, which provides a proof-of-principle demonstration of the theory.