title: Coupled quantum Otto cycle.
abstract: We study the one-dimensional isotropic Heisenberg model of two spin-1/2 systems as a quantum heat engine. The engine undergoes a four-step Otto cycle where the two adiabatic branches involve changing the external magnetic field at a fixed value of the coupling constant. We find conditions for the engine efficiency to be higher than in the uncoupled model; in particular, we find an upper bound which is tighter than the Carnot bound. A domain of parameter values is pointed out which was not feasible in the interaction-free model. Locally, each spin seems to cause a flow of heat in a direction opposite to the global temperature gradient. This feature is explained by an analysis of the local effective temperature of the spins.
authors.affiliation: Indian Institute of Science Education and Research Mohali Transit Campus: MGSIPAP Complex, Sector 26, Chandigarh 160019, India. george@iisermohali.ac.in
authors.forename: George
authors.initials: G
authors.lastname: Thomas
authors.forename: Ramandeep S
authors.initials: RS
authors.lastname: Johal