Quantum heat engines (QHEs) employing Otto, Carnot, and Szilard cycles have already been demonstrated. Experimental demonstration of the quantum Stirling engine has been hindered due to the challenges in realizing a quantum isothermal process with qubits. Here, we experimentally execute a single-ion Stirling QHE and demonstrate that its efficiency is enhanced when dephasing is involved during the heat release strokes, which is contrary to the conventional viewpoint that dephasing deteriorates quantum features, resulting in reduced performance in QHEs. We also observe periodic oscillations in the heat absorption and the efficiency of the Stirling QHE, indicating the involvement of quantum coherence in the engine cycles. Our experiment is the first execution of Stirling QHE in a spin system, which may help better understand quantum thermodynamics and open new possibilities toward harnessing decoherence as a resource to improve the performance of QHEs.

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• Quantum engineering
• Quantum heat engines & refrigerators
• Trapped ions