Activating thermally charged quantum batteries in finite time: Thermodynamic trade-offs between correlations, work, and information

Quantum batteries are often limited by their fragility, leading researchers to consider thermally charged states—which are stable but passive—as a resource. The central challenge is how to efficiently transform these passive states into active ones from which useful energy can be extracted, while accounting for the energetic and entropic costs of the activation process itself.

The authors propose a stirring protocol where a thermally charged quantum battery (a harmonic oscillator) is coupled to an auxiliary system (an activator) via a time-dependent Hamiltonian. This process generates correlations between the two systems, which are essential for converting the passive battery state into an active one. The study derives thermodynamic bounds on the net extractable energy (net ergotropy) by explicitly calculating the work cost of the stirring, the entropic cost of correlation generation, and the information gained through projective measurements on the activator. The performance is analyzed using a waveguide-QED setup.

The study establishes that the activation of a thermally charged battery is a thermodynamic trade-off between the energy input, the entropy production associated with correlations, and the information extracted via measurement. The researchers show that net energy extraction is possible when the battery and activator are initially at different temperatures. Furthermore, they demonstrate that performing a projective measurement on the activator after the stirring phase allows for outcome-conditioned unitary operations, which significantly increases the total extractable energy compared to protocols without feedback.