  Recently, the studies on the light-matter interaction have been pushed into
the ultrastrong coupling regime, which motivates the exploration of
applications of the counter rotating wave (CRW) interaction. Even in the
ultrastrong coupling regime, however, few photons can be generated from the
vacuum by switching on the CRW interaction. Here we propose a scheme to enhance
the photon generation from the vacuum by a bang-bang (switching on/off) control
of the CRW interaction. By developing a pruning greedy algorithm to search the
optimal control sequence, we find that the maximum photon number obtained for a
given time period in our scheme can be dramatically increased up to several
orders than that from switching on the CRW interaction.
