PXP model — non-thermal revivals from Néel state in Rydberg chain
The PXP model describes Rydberg atoms with nearest-neighbor blockade: H_PXP = Σ P_{i-1} X_i P_{i+1}, where P=(1-|r⟩⟨r|)/2 projects out doubly-excited neighbors. Starting from the Néel state |↑↓↑↓...⟩, the system shows anomalous revivals — quantum many-body scars — violating ETH. Ergodic (random) initial states thermalize. The scar states form an approximate SU(2) tower embedded in an otherwise chaotic spectrum.