Comment on “Loss-Free Excitonic Quantum Battery”

Abstract

In Ref. [J. Liu, D. Segal, and G. Hanna. J. Phys. Chem. C, 123, 18303 (2019)] there is a novel proposal of a quantum battery based on environmental interaction. The system studied is a para-Benzene ring with a symmetry that is broken in order to "redistribute the energy" creating a population imbalance between the sites. In this paper, the dynamics of the system is calculated under the single-excitation approximation and there is no discussion about its energetics. We do not discuss the authors' approach or numerical results on the single-excitation framework, but we would like to point out that observing the single-excitation populations is insufficient to obtain any information about the system's energetics. Since an infinite probe is attached to break the symmetries, it not only redistributes the energies as the authors suggest but the environment also exchanges energy with the system. Moreover, the accumulation of a single-excitation population at a specific site does not ensure that this site has more energy that can be extracted to do useful work. Thus, despite their single-excitation populations being correct, the para-Benzene's energetics do not behave as a battery.