Quantum many-body scar states with emergent kinetic constraints and finite-entanglement revivals

Strongly interacting systems with quantum many-body scars exhibit persistent fidelity oscillations when prepared in a certain class of initial states, but otherwise undergo ergodic dynamics. Previous examples of scars have interpreted the characteristic periodic dynamics in terms of the precession of a macroscopic SU (2) spin in an effective magnetic field. Here, the authors uncover a new exactly solvable example of many-body scars in a spin- model and show that the scarred dynamics in this model evades such an interpretation. This unusual coherent dynamics arises due to an emergent kinetic constraint that endows the time-evolving many-body state with constant area-law entanglement. The model studied in this work is relevant to experiments on Rydberg-atom quantum simulators in the antiblockade regime.