Isolated quantum systems are expected to thermalize — initial conditions are forgotten as the system relaxes to a thermal state. Quantum many-body scars violate this expectation. Certain initial states exhibit persistent revivals, returning periodically to near their starting configuration while the rest of the spectrum thermalizes normally. The scar states are nonthermal islands in an ergodic sea.
Hardcore bosons on a pi-flux ladder generate exact scars through kinetic frustration (arXiv:2603.11191). The magnetic flux threading the ladder creates destructive interference that forbids certain hopping paths, confining particle motion. This frustration produces exact (not approximate) scar states — the revivals persist indefinitely rather than decaying slowly.
The model is minimal enough for cross-platform implementation. Cold atom Bose-Hubbard simulators realize it through optical lattice geometry. Rydberg atom tweezer arrays realize it through blockade constraints that mimic hardcore exclusion. The same scars appear on both platforms because the frustration mechanism — destructive interference from magnetic flux — maps onto the natural constraints of each system.
Scar lifetimes can be extended by tuning Hubbard interactions or applying Floquet drives. The practical heuristic for finding optimal parameters uses eigenstate energy distributions — broader distributions in the scar subspace predict shorter lifetimes. The heuristic replaces exhaustive parameter sweeps with a diagnostic that can be computed before running the experiment.
Frustration doesn't merely slow thermalization. It creates states that never thermalize — exact nonthermal eigenstates embedded in an otherwise thermal spectrum.