We demonstrate proximity-induced localization and re-entrant delocalization in a detuned quasiperiodic ladder. In the weak-quasiperiodic regime, where uncoupled Aubry-André chains are extended, a staggered detuning applied to only one leg induces localization in the neighboring leg through inter-leg hybridization. With further increasing detuning, the pure chain re-enters a delocalized regime, producing a delocalized-localized-delocalized sequence without directly modifying its quasiperiodic potential. We identify these regimes using static localization diagnostics and demonstrate experimentally accessible dynamical signatures on IBM Quantum hardware: strongly suppressed wavefunction spreading in the proximity-localized regime and its re-entrant recovery at larger detuning. These results establish leg-selective detuning as a programmable control knob for inducing and reversing localization in coupled quasiperiodic systems.
We demonstrate proximity-induced localization and re-entrant delocalization in a detuned quasiperiodic ladder. In the weak-quasiperiodic regime, where uncoupled Aubry-André chains are extended, a staggered detuning applied to only one leg induces localization in the neighboring leg through inter-leg hybridization. With further increasing detuning, the pure chain re-enters a delocalized regime, producing a delocalized-localized-delocalized sequence without directly modifying its quasiperiodic potential. We identify these regimes using static localization diagnostics and demonstrate experimentally accessible dynamical signatures on IBM Quantum hardware: strongly suppressed wavefunction spreading in the proximity-localized regime and its re-entrant recovery at larger detuning. These results establish leg-selective detuning as a programmable control knob for inducing and reversing localization in coupled quasiperiodic systems.
This work reports rich localization-delocalization transitions in a quasiperiodic ladder, of which the two legs are subject to the same quasiperiodic onsite potential but can be shifted laterally relative to each other. It is found that the lateral shift between the two legs effectively generates a magnetic flux in the reciprocal momentum space. The lateral shift thus offers a control knob, allowing us to access and simulate rich phenomena including magnetic-flux-enhanced localization, magnetic-flux-suppressed localization, and magnetic-flux-induced reentrant localization transitions. The underlying physical mechanisms as well as the phase boundaries separating localized, mixed, and extended phases are both qualitatively and quantitatively understood, based on a band-structure analysis that employs a commensurate approximation to the quasiperiodic potential, requiring only unit cells of small to modest sizes. Our work provides a highly tunable platform for exploring localization physics with promising applications such as quantum switching, and a broadly applicable approach for understanding localization-delocalization transitions in quasiperiodic systems.
Periodic driving provides a powerful route for controlling localization and engineering effective Hamiltonians in quantum systems. A localized one-dimensional Aubry-André chain can be driven into a fully delocalized phase when the entire system is driven below a critical frequency. Here, we ask whether such delocalization can be achieved by driving only a part of the system. We address this question using a two-leg ladder comprising an Aubry-André chain coupled to a periodically driven clean tight-binding chain. Exact numerical calculations show that, starting from a localized static ladder, subsystem driving below a critical frequency cannot achieve complete delocalization. Instead, a mixed phase emerges, with localized and delocalized states coexisting and the fraction of delocalized states varying nonmonotonically with the driving frequency. This behavior can be understood using local effective Hamiltonians. Although these effective Hamiltonians are derived analytically in the high-frequency regime, they can nevertheless predict the localization transition occurring in the moderate-frequency regime. In fact, by quantifying the emergent nonlocality of the Floquet Hamiltonian, we show that these effective Hamiltonians provide a valid description up to a crossover frequency that is lower than the critical frequency associated with the localization transition. Our results demonstrate an alternative route to Floquet engineering, in which the transport properties of a quantum lattice system can be modified by driving only a subsystem.
We investigate the interplay between the non-Hermitian skin effect and Aubry-André-Harper (AAH) quasiperiodic disorder in a one-dimensional Su-Schrieffer-Heeger (SSH) chain with nonreciprocal hopping. By exact diagonalization, transfer-matrix analysis, and an analytical similarity-transformation argument, we map the full ( , δ) phase diagram, where A is the AAH modulation strength and the nonreciprocity parameter. We identify five distinct regimes: ( ) topological with extended bulk, (II) AAH-localized, (III) skin-localized, (IV) fully localized, and a previously unreported (V) competition regime exhibiting reentrant partial delocalization, in which intermediate quasiperiodic disorder disrupts the directional skin accumulation before ultimately Anderson-localizing all states. Using phase-averaged diagnostics and finite-size scaling, we confirm that the reentrant regime is robust, characterized by a non-monotonic inverse participation ratio that sharpens with increasing system size. We derive an analytical expression for the modified localization boundary λc(δ)=2veffw with vvff=v2−δ2, which agrees with numerical Lyapunov exponent calculations. We further show that quasiperiodic disorder progressively unwinds the complex spectral loops, destroying the point-gap topology at a critical strength distinct from the band-topological transition ; that the skin effect suppresses entanglement entropy to near-zero values while sufficiently strong AAH disorder partially restores it ; and that the SSH sublattice structure absent in the widely studied non-Hermitian AAH chain is essential for producing the five-phase landscape, as demonstrated by direct comparison with the non-dimerized limit.
We study interaction-induced localization in a spinful quasiperiodic Hubbard ring with quasiperiodically modulated hopping and a staggered spin-dependent Zeeman field using a self-consistent Hartree-Fock approach. We characterize localization through the inverse participation ratio, normalized participation ratio, and multifractal analysis, and further examine its signatures in self-consistent real-space observables, including double occupancy, density fluctuations, local entropy, spin-density-wave order, and related correlation measures. As the Hubbard interaction is increased, we find a nonmonotonic evolution of the eigenstates: an initially extended regime gives way to an intermediate localized phase, followed by reentrant delocalization at stronger interactions. The width of this intermediate regime grows systematically with both the quasiperiodic hopping amplitude and the staggered Zeeman-field strength, indicating a cooperative enhancement of localization by these two ingredients. In the localized regime, the self-consistent interaction produces pronounced spin dependence in both the spectra and localization properties, resulting in distinct responses of the spin-up and spin-down sectors. The interaction-driven crossover is consistently captured by the real-space observables and further corroborated by real-time wave-packet dynamics, which reveal successive ballistic, confined, and reentrant-transport regimes consistent with the underlying eigenstate character. These results provide a unified framework for understanding the interplay of quasiperiodicity, electronic interactions, and spin-dependent fields in controlling localization, criticality, and quantum transport in correlated quasiperiodic systems.
Low-dimensional quasiperiodic systems exhibit localization transitions by turning all quantum states localized after a critical quasidisorder. While certain systems with modified or constrained quasiperiodic potential undergo multiple localization transitions in one dimension, we predict an emergence of multiple localization transitions without directly imposing any constraints on the quasiperiodic potential. By considering a one-dimensional system described by the Aubry-Andr\'e model, we show that an additional staggered on-site potential can drive the system through a series of localization transitions as a function of the staggered potential. Interestingly, we find that the number of localization transitions strongly depends on the strength of the quasiperiodic potential. Moreover, we obtain the signatures of these localization transitions in the expansion dynamics and propose an experimental scheme for their detection in the quantum gas experiment.
We study the quench dynamics of two bosons possessing on-site repulsive interaction on a two-leg ladder and show that the presence of uniform flux piercing through the plaquettes of the ladder favors the localization of the bound states in the dynamics. We find that, when the two bosons are symmetrically initialized on the edge rung of the ladder, they tend to edge-localize in their quantum walk, a phenomenon which is not possible in the absence of flux. However, when the bosons are initialized on the bulk rung they never localize and exhibit linear spreading in their quantum walk. Interestingly, however, we find that, in the later case, a finite flux favors localization of the bulk bound states in the presence of sufficiently weak quasiperiodic disorder, which is otherwise insufficient to localize the particles in the absence of flux. In both cases, we obtain that the localization in the dynamics strongly depends on the combined effect of the flux and interaction strengths, as a result of which we obtain a signature of reentrant delocalization as a function of flux (interaction) for fixed interaction (flux) strengths.