Tunable information insulation induced by constraint mismatch

TL;DR

This paper investigates how constraining and relaxing junctions in coupled 1D PXP chains can control quantum information flow, Hilbert space fragmentation, and the emergence of protected zero-energy modes, with implications for Rydberg atom experiments.

Contribution

It introduces a composite model of constrained PXP chains with tunable junctions, revealing information insulation, Hilbert space fragmentation, and protected zero modes.

Findings

Junction constraints act as infinite barriers to quantum information exchange.

Multiple frozen junctions fragment the Hilbert space exponentially.

A chirally protected zero-energy mode exists with edge and bulk peaks.

Abstract

We study a composite model of two $1D$ $PXP$ chains with dual constraints, forming a junction that acts as an infinite kinematic barrier to quantum information exchange. Moreover, the hard wall at the junction which acts as a perfect reflector, preventing any quantum information leakage between the two sides of the composite chain, can be made permeable by relaxing the constraint at the junction sites. Multiple frozen junctions shatter the Hilbert space into disjoint Krylov fragments, the number of which increases exponentially with the engineered defects. Furthermore, the energy level statistics in each symmetry-resolved sector are strictly Poissonian, demonstrating that the tensor sum of the disjoint Hamiltonians results in a pure superposition of the chaotic spectra of the sub- $PXP$ chains. We also find that a chirally protected zero-energy mode can exist which has local peaks at the physical edges and within the bulk near the junction sites. This state is protected from hybridization with bulk states induced by any chirality preserving disorder. Due to the tensor product structure of the eigenfunctions, the non-zero energy scar states also multiply in number. Finally, we introduce novel Fock states with spatially tunable thermal and athermal regions. This architecture can be readily realized in programmable Rydberg atom platforms using optical tweezers, addressing beams and facilitation techniques.