ICTS

The study of thermalization and its breakdown in isolated quantum systems is a fascinating area of research. In many-body localized (MBL) systems, emergent quasilocal conserved charges prevent thermalisation. The stability of the MBL phase in interacting disordered systems at thermodynamic limit is currently under intense scrutiny. So, a natural question is whether MBL-type physics can occur in translationally invariant systems. This question has motivated the study of various kinetically constrained spin-chains without quenched disorder, a prominent example being the quantum East model. For the 1D quantum East model with open boundary condition, we show that in the limit $s \to -\infty$, the ground state is approximately captured by a simple spin-polarized product state. The polarization angle changes as we approach the quantum phase transition at $s = 0$ where the ground state becomes an exact product state polarized along the X-axis. For $s \to -\infty$, we further identify a low-entanglement excited eigenstate that differs from the ground state only by a $\pi$-rotation of the first spin and is well approximated by a spin-coherent state. For $-1\lesssim s<0$, this spin-coherent state overlaps mainly with two eigenstates separated by a system size-independent energy gap, leading to long-lived coherent oscillations of local observables near the edge. These oscillations originate from boundary physics and are distinct from quantum many-body scars and hypercube-like Fock-space mechanisms.