PAPER

With the progress of nano-technology, thermodynamics also has to be scaled down, calling for specific protocols to extract andmeasurework. Usually, such protocols involve the action of an external, classicalfield (the battery) of infinite energy, that controls the energy levels of a small quantum system (the calorific fluid).Herewe suggest a realistic device to reversibly extract work in a battery offinite energy: a hybrid optomechanical system. Such devices consist of an optically active two-level quantum system interacting strongly with a nano-mechanical oscillator that provides and storesmechanical work, playing the role of the battery.We identify protocols where the battery exchanges large, measurable amounts of workwith the quantum emitter without getting entangledwith it.When the quantumemitter is coupled to a thermal bath, we show that thermodynamic reversibility is attainable with state-of-the-art devices, paving the road towards the realization of a full cycle of information-to-energy conversion at the single bit level. 1