Heat going from cold to hot… is there a demon in my system? A quantum system is proposed able to revert a heat current, making it go from the coldest to the hottest spot in a device. It does it by interacting with two other close by spots that are neither as hot nor as cold. Furthermore, it does so by not exchanging any energy with the working system, exactly as a Maxwell demon would do. Maxwell demons are ideal creatures that challenged our understanding of thermodynamics for decades during the last century. By getting access to the properties of single particles in a gas, the demon is able to do specific operations that are able to produce a useful thermodynamic operation (such as cooling) apparently at no cost (except for the troubles in processing the acquired information). Nowadays, nanoscopic devices can be developed whose properties are affected by changes of a single particle (single electron quantum dots, qubits…), so proposals have been done that use these systems as electronic analogues of Maxwell demons able to work autonomously, with a few experiments having verified the basic principles. To do so, the demon must be fueled by a nonequilibrium situation. This way the correspondence between the exchange of information and of thermodynamic quantities has been established. Our work proposes the first autonomous demon able to work on photonic reservoirs mediated by the coupling of two qutrits. Despite its operation being indistinguishable from that of a Maxwell demon, it avoids any clear interpretation in terms of information processing by the demon, challenging the classification of demonic nanoscale engines and introducing new ways to process heat onchip in quantum information processors. [Full article]
