Fate of emergent Hilbert space fragmentation and information insulation upon softening of hard dual constraints at PXP-chain junctions

Abstract:We demonstrate emergent Hilbert-space fragmentation in a composite chain of PXP and dual-PXP subchains separated by junctions with simultaneous blockade and anti-blockade projection constraints. The Hilbert space shatters into disjoint Krylov fragments growing exponentially with junction number. Freezing does not require a unique allowed junction state: multiple configurations remain locally allowed, but the dual constraints remove dynamical links between them. Each fragment is labeled by frozen junction configurations and contains compatible basis states. This fragmentation produces dynamical caging of quantum information between neighboring junctions and novel states with partially thermal and athermal regions. Softening the junction by admitting other local states with variable nonzero diagonal amplitudes destroys the direct-sum block structure and fragmentation. Nevertheless, information remains dynamically insulated and inhomogeneous thermal properties persist up to an onset time scaling with the diagonal energy penalty of the previously restricted junction states, followed by longer prethermal behavior. Energy-level statistics in each symmetry-resolved sector evolve from Poissonian in the hard-junction limit toward Wigner-Dyson behavior upon softening, with finite-size non-monotonicity. This signals the breakdown of the tensor-sum structure yielding pairwise sums of chaotic subchain spectra, restoring chaotic thermalization. In the hard-junction case, we find a chirally protected zero-energy mode with density peaks at physical edges and near the junction, pinned to zero under chirality-preserving disorder. The tensor-product eigenfunction structure also enhances the number of nonzero-energy scar states. Finally, we discuss routes to these junction architectures in programmable Rydberg atom platforms using optical tweezers, local addressing, and facilitation techniques.

Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)

arXiv:2604.00732 [cond-mat.stat-mech]

(or arXiv:2604.00732v3 [cond-mat.stat-mech] for this version)

https://doi.org/10.48550/arXiv.2604.00732 Focus to learn more arXiv-issued DOI via DataCite

arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website.

Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them.

Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs.