  Recent experiments have demonstrated that molecular polaritons, hybrid states
of light and matter formed by the strong coupling between molecular electronic
or vibrational excitations and an optical cavity, can substantially modify the
physical and chemical properties of molecular systems. Here, we show that, by
exploiting the collective character of molecular polaritons in conjunction with
the effect of polaron decoupling, i.e., the suppression of environmental
influence on the polariton, a superreaction can be realized, involving a
collective enhancement of charge or excitation-energy transfer reaction rate in
a system of donors all coupled to a common acceptor. This effect is analogous
to the phenomenon of superradiation. Since the polariton is a superposition
state of excitations of all the molecules coupled to the cavity, it is
vulnerable to the effect of decoherence caused by energy fluctuations in
molecular systems. Consequently, in the absence of a strong light-matter
interaction, the reaction rate decreases significantly as the number of
molecules increases, even if the system starts from the polariton state. By
turning on the light-matter interaction, the dynamic behavior of the system
changes dramatically, and the reaction rate increases with the number of
molecules, as expected for a superreaction. The underlying mechanism is shown
to be the enhancement of quantum coherence between different donors as the
light-matter interaction becomes stronger.
