How do I add 1+1 using a photonic computer?

Question

A similar question has been previously asked & has an excellent answer discussing half, full & ripple carry adders. I am curious to find out how these adders would be constructed in the setting of photonic quantum computers (eg. with continuous variable qumodes instead of qubits).

Answer 1

You would focus on repeatedly making copies of the state $|000000\rangle + |111111\rangle$, which you can then dynamically stitch into a 3d cluster state with fusion measurements. Once you have a cluster state, you can do fault tolerant Clifford gates by introducing topological defects at the right places and times. Add some sort of magic state injection mechanism and you have universal gate based computation via distillation + gate teleportation. At which point you can do the Toffoli gates and etc from the other 1+1 question you referenced.

PsiQuantum has a bunch of papers explaining the pieces of this specifically in the context of photons:

• Interleaving: Modular architectures for fault-tolerant photonic quantum computing
• Logical blocks for fault-tolerant topological quantum computation
• Unifying flavors of fault tolerance with the ZX calculus
• Fault-tolerant Post-Selection for Low Overhead Magic State Preparation