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Title: Why the Rydberg-blockade chain shows persistent revivals
Plain: In chains of Rydberg atoms where neighbours cannot both be excited, one special initial pattern keeps returning to itself instead of thermalizing. The underlying reason is not fully understood.
Precise: In the PXP model $H = \Omega \sum_i P_{i-1} X_i P_{i+1}$ (P the projector onto the atomic ground state, X the Pauli flip), the period-2 density-wave $(\mathrm{Z2})$ state shows revivals carried by a tower of special eigenstates with nearly equal energy spacing. Explain the origin of this tower (broken $\operatorname{su}(2)$ algebra, semiclassical periodic orbit, or proximity to an integrable point) in a form that predicts the revival frequency and decay rate. Answer: a theory with quantitative predictions for both.
Settled by: A derivation predicting revival frequency and damping to within a few percent, tested against numerics at $L \ge 30$.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2017