# Quantum absorption refrigerator with trapped ions

## TL;DR

This paper reports the experimental realization of a quantum absorption refrigerator using three trapped ions, demonstrating quantum cooling below classical limits and exploring quantum resources like squeezing.

## Contribution

It presents the first experimental implementation of a quantum absorption refrigerator with trapped ions, including analysis of quantum resources and performance in single-shot regimes.

## Key findings

- Successful cooling below classical thermodynamic limits.
- Quantum resources like squeezing enhance refrigeration.
- Performance demonstrated in steady-state and single-shot regimes.

## Abstract

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.