New exact eigenstates in the Lesanovsky model, proximity to integrability and the PXP model, and approximate scar states

Cold Rydberg atoms have received significant recent attention. We study a model of Rydberg atoms in a nearest-neighbor Rydberg blockaded regime, introduced by Lesanovsky in Phys. Rev. Lett. 108, 105301 (2012). This many-body model (which has one parameter z) has an exactly known gapped, liquid ground state, and two exactly known low-lying excitations. We discover two new exact low-lying eigenstates. We also discuss behavior of the model at small parameter z and its proximity to an integrable model. Lastly, we discuss connections between the PXP and Lesanovsky models at intermediate z. The PXP model describes a recent experiment that observed unusual revivals from a charge density wave initial state, which are attributed to a set of many-body "scar states" which do not obey the eigenstate thermalization hypothesis. We discuss the possibility of scar states in the Lesanovsky model.