Collective charging of an organic quantum battery

We study the collective charging of a quantum battery (QB) consisting of a one-dimensional molecular aggregate and a coupled single-mode cavity, to which we refer to as an "organic quantum battery" since the battery part is an organic material. The organic QB can be viewed as an extension of the so-called Dicke QB [D. Ferraro et al., Phys. Rev. Lett. 120, 117702 (2018)0031-900710.1103/PhysRevLett.120.117702] by including finite exciton hopping and exciton-exciton interaction within the battery. We consider two types of normalizations of the exciton-cavity coupling when the size of the aggregate N is increased: (I) the cavity length also increases to keep the density of monomers constant, and (II) the cavity length does not change. Our main findings are the following. (i) For fixed N and exciton-cavity coupling, there exist optimal exciton-exciton interactions at which the maximum stored energy density and the maximum charging power density reach their respective maxima that both increase with increasing exciton-cavity coupling. The existence of such maxima for weak exciton-cavity coupling is argued to be due to the nonmonotonic behavior of the one-exciton to two-exciton transition probability in the framework of second-order time-dependent perturbation theory. (ii) Under normalization I, no quantum advantage is observed in the scaling of the two quantities with varying N. Under normalization II, it is found that both the maximum stored energy density and the maximum charging power density exhibit quantum advantages compared with the Dicke QB.