Quantum Battery: Ergotropy & Coherent Charging

A quantum battery — an ensemble of two-level cells charged by a driving field — stores energy that is not always fully recoverable. This simulator drives N battery cells with a resonant Rabi field under pure dephasing and tracks two distinct quantities in real time: the total stored energy and the ergotropy, the maximum work actually extractable by a unitary operation. As dephasing scrambles the cells' quantum coherence, a growing gap opens between the two — energy that is stored but thermodynamically stranded as "passive" energy. A toggle between individually-driven and Dicke-style collectively-driven charging shows the well-known quantum speed-up in charging power that collective coupling provides.