  The four-component cat state represents a particularly useful quantum state
for realizing fault-tolerant continuous variable quantum computing. While such
encoding has been experimentally generated and employed in the microwave
regime, the states have not yet been produced in the optical regime. Here we
propose a simple linear optical circuit combined with photon counters for the
generation of such optical four-component cat states. This work might pave the
way for the first experimental generation of fault-tolerant optical continuous
variable quantum codes.
