Coherence-powered work exchanges between a solid-state qubit and light fields
Résumé
How does quantum coherence impact energy exchanges between quantum systems? This key question of quantum thermodynamics is also of prime importance for the energy management of emerging technologies based on quantum coherence. Pioneering theoretical frameworks have been proposed to describe the role of coherence in the energetic exchanges between a qubit and the electromagnetic field. Here, we experimentally study the work transferred during the spontaneous emission of a solid-state qubit into a reservoir of modes of the electromagnetic field, a step that energetically corresponds to the charging of a quantum battery. We show that the amount of transferred work is proportional to the initial quantum coherence of the qubit, and is reduced at higher temperatures. In a second step, we {study the discharge of the battery and its energy transfer} to a classical, i.e., laser field using homodyne-type measurements. Our research shows that the amount of energy and work transferred to the laser field is controlled by the relative classical optical phase between the two fields, the quantum purity of the charged battery field as theoretically predicted, as well as long-term fluctuations in the qubit solid-state environment. Our study lays the groundwork for the energetics of quantum light generation and optical quantum interferences - two key processes that are at the core of most light-based quantum technologies.