  This article reviews recent hybrid approaches to optical quantum information
processing, in which both discrete and continuous degrees of freedom are
exploited. There are well-known limitations to optical single-photon-based
qubit and multi-photon-based qumode implementations of quantum communication
and quantum computation, when the toolbox is restricted to the most practical
set of linear operations and resources such as linear optics and Gaussian
operations and states. The recent hybrid approaches aim at pushing the
feasibility, the efficiencies, and the fidelities of the linear schemes to the
limits, potentially adding weak or measurement-induced nonlinearities to the
toolbox.
