Collective enhancements in charging quantum batteries via a quantum heat engine*

As a model of so-called quantum battery, a quantum system as an energy storage, we study the charging of many two-level systems via a quantum heat engine. Especially, we focus on the collective effects in the charging. We show that the collective charging outperforms in the amount of the stored energy, its fluctuation, and the charging speed in comparison to the individual one. In the collective charging, symmetry of the interaction between the engine and the battery causes emergent bosonic quantum statistics, which result in a collective high probability excitation.