Figure 4
From: Transport of Photonic Bloch Wave in Arrayed Two-Level Atoms
Feynman diagrams. (a) Feynman diagram of \(\langle i|{\mathscr{U}}(t)|i\rangle \) which is the direct propagation of a two-level atom at site i to itself after a time evolution t. (b) Feynman diagram of \(\langle \,j\ne i|{\mathscr{U}}(t)|i\rangle \) which is the indirect propagation of a two-level atom at site i to a different site j after a time evolution t through emitting and absorbing a photon. (c) Feynman diagram of \(\langle \gamma ({x}_{j})|{\mathscr{U}}(t)|i\rangle \) which is the spontaneous emission of a two-level atom at site i emitting a photon to j after a time evolution t.
