New quantum heat engine simultaneously produces work and refrigeration

Researchers at Qufu Normal University, the University of Hong Kong and the University of Palermo observed an anomalous thermal effect that allows a quantum system to absorb heat from colder thermal reservoirs.

As the team described in Physical Review Letters , this unusual effect informed the creation of a new quantum Otto engine.

“Indefinite causal order (ICO) allows two events to occur in a superposition of orders,” Zhong-Xiao Man, co-senior author of the paper, commented.

“In quantum thermodynamics, these events are modelled as thermalisation channels acting on a system via a control qubit, creating an indefinite order. Previous work showed that even with identical channel temperatures, the system need not equilibrate to that temperature—a striking deviation from standard thermodynamics. Motivated by this, we asked: What happens to heat flow when the system and channels start at different temperatures?”