In recent years substantial efforts have been expended in extending thermodynamics to single quantum systems. Quantum effects have emerged as a resource that can improve the performance of heat machines. However in the fully quantum regime their implementation still 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 made possible by coherence and demonstrate cooling below both the steady-state energy and a benchmark set by classical thermodynamics.

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We report an experimental study of peak and phase-space density of a two-stage magneto-optical trap (MOT) of 6 Li atoms, which exploits the narrower 2S 1/2 → 3P 3/2 ultraviolet (UV) transition at 323 nm following trapping and cooling on the more common D2 transition at 671 nm. The UV MOT is loaded from a red MOT and is compressed to give a high phase-space density up to 3 × 10 −4 . Temperatures as low as 33 μK are achieved on the UV transition. We study the density limiting factors and in particular find a value for the light-assisted collisional loss coefficient of 1.3 ± 0.4 × 10 −10 cm 3 /s for low repumping intensity.