A simple proof of unitary parallelization via port-based teleportation

Port-based teleportation (PBT) is a variant of quantum teleportation that does not require corrections on the teleported state: starting with $N$ shared EPR states, Alice can teleport a qudit to Bob by performing a measurement on her system and informing Bob which of his $N$ `ports’ to retrieve the state, up to infidelity decaying with $N$. Existing quantum circuits of PBT rely on representation theory tools and the mixed Schur transform. In this note, we report an elementary efficient circuit for PBT, which has depth $\mathrm{polylog}(N,d)$. As a corollary, this gives a simple proof that all $n$-qubit unitaries can be parallelized to $\mathrm{poly}(n)$ depth, recovering a recent result due to Nehoran–Slote–Yuen and OpenAI.