Scar-induced imbalance in staggered Rydberg ladders

We demonstrate that the kinematically constrained model of Rydberg atoms on a two-leg ladder with staggered detuning, $\mathrm{\ensuremath{\Delta}}\ensuremath{\in}[0,1]$, has quantum many-body scars (QMBSs) in its spectrum and represents a nonperturbative generalization of the paradigmatic PXP model defined on a chain. We show that these QMBSs result in coherent many-body revivals and site-dependent magnetization dynamics for both N\'eel and Rydberg vacuum initial states around $\mathrm{\ensuremath{\Delta}}=1$. The latter feature leads to eigenstate thermalization hypothesis (ETH)-violating finite imbalance at long times in a disorder-free system. This is further demonstrated by constructing appropriate local imbalance operators that display nonzero long-time averages for N\'eel and vacuum initial states. We also study the fidelity and Shannon entropy for such dynamics which, along with the presence of long-time finite imbalance, brings out the qualitatively different nature of QMBSs in PXP ladders with $\mathrm{\ensuremath{\Delta}}\ensuremath{\sim}1$ from those in the PXP chain. Finally, we identify additional exact midspectrum zero modes that stay unchanged as a function of $\mathrm{\ensuremath{\Delta}}$ and violate ETH.