What you’re seeing: each arrow is one random path. We compute its action S, set its angle θ = S/ħ, and add it tip‑to‑tail. Near‑classical paths (lowest action in the batch) point similarly and reinforce. Far‑from‑classical paths rotate wildly and cancel out.
Purple line: the resultant vector in the complex plane (right panel). Its length is |ΣA|. The plotted probability is |ΣA|² / N² (normalized by sample count).