  The development of quantum information processing has traditionally followed
two separate and not immediately connected lines of study. The main line has
focused on the implementation of quantum bit (qubit) based protocols whereas
the other line has been devoted to implementations based on high-dimensional
Gaussian states (such as coherent and squeezed states). The separation has been
driven by the experimental difficulty in interconnecting the standard
technologies of the two lines. However, in recent years, there has been a
significant experimental progress in refining and connecting the technologies
of the two fields which has resulted in the development and experimental
realization of numerous new hybrid protocols. In this Review, we summarize
these recent efforts on hybridizing the two types of schemes based on discrete
and continuous variables.
