  The interaction of a three-level atom with the electromagnetic field of a
quantum cavity in the presence of a laser field presents a rich behavior that
we exploit to discuss two quantum batteries. In the first setup, we consider a
single three-level atom interacting sequentially with many cavities, each in a
thermal state. We show that under this process, the atom converges towards an
equilibrium state that displays population inversion. In the second setup, a
stream of atoms in a thermal state interacts sequentially with a single cavity
initially in a thermal state at the same temperature as the atoms. We show that
the cavity's energy increases continuously as the stream of atoms continues to
cross, and the cavity does not reach an equilibrium state. However, if we
consider the state after many atoms have traveled, the cavity is in an active
state that stores energy. The charging process we propose is robust. We discuss
its thermodynamics and evaluate the energy supplied by the laser, the energy
stored in the battery, and, thus, the device's efficiency.

Quantum Physics