  Thermodynamics is one of the oldest and well-established branches of physics
that sets boundaries to what can possibly be achieved in macroscopic systems.
While it started as a purely classical theory, it was realized in the early
days of quantum mechanics that large quantum devices, such as masers or lasers,
can be treated with the thermodynamic formalism. Remarkable progress has been
made recently in the miniaturization of heat engines all the way to the single
Brownian particle as well as to a single atom. However, despite several
theoretical proposals, the implementation of heat machines in the fully quantum
regime remains a challenge. Here, we report an experimental realization of a
quantum absorption refrigerator in a system of three trapped ions, with three
of its normal modes of motion coupled by a trilinear Hamiltonian such that heat
transfer between two modes refrigerates the third. We investigate the dynamics
and steady-state properties of the refrigerator and compare its cooling
capability when only thermal states are involved to the case when squeezing is
employed as a quantum resource. We also study the performance of such a
refrigerator in the single shot regime, and demonstrate cooling below both the
steady-state energy and the benchmark predicted by the classical thermodynamics
treatment.
