Nonlinear interaction between the modes of motion in the trapped ion system is required for implementation of the heat machines and can be induced by the anharmonicity of the Couloumb interaction between the ions. Using three modes of ions motion as the heat bodies we experimentally realized a quantum absorption refrigerator in a system of three trapped ions. Three normal modes of motion are coupled by a trilinear Hamiltonian such that heat transfer between two modes refrigerates the third. This system allows us to investigate dynamics and steady-state properties of the refrigerator and study the performance of such refrigerator in the regime where quantum effects become important .
Fig. 1. Direction of heat flow in the absorption refrigerator. Energy from the work body is transferred to the hot body, which removes energy from cold body. The black arrows label the ion's motional eigenmodes utilized as heat bodies.