  Quantum energy science is rapidly emerging as a domain interested in the
generation, transfer and storage of energy at the quantum level. In particular,
quantum batteries have the scope to exploit the wonders of quantum mechanics in
order to boost their performance as compared to their electrochemical
equivalents. Here we show how an exponential enhancement in stored energy can
be achieved with a quantum battery thanks to a two-photon charging protocol. We
consider theoretically a quantum battery modelled as a quantum harmonic
oscillator, which when driven by a quadratic field (manifested by a Gaussian
pulse envelope) gives rise to squeezing of the battery. This quantum squeezing
ensures that the population of the battery is driven exponentially up its
bosonic energy ladder. Our results demonstrate a plausible mechanism for
quickly storing a vast amount of energy in a quantum object defined by
continuous variables, which may be explored experimentally in a variety of
quantum optical platforms.
