Many-Body Localization in the Infinite-Interaction Limit

We study the full many-body localization (MBL) in the Rydberg atomic quantum simulator with quasiperiodic modulation. Employing both exact diagonalization (ED) and time-evolving block decimation (TEBD) methods, we identify evidence of a constrained many-body-localized phase stabilized by a pure quasirandom field transverse to the direction of the projection. Intriguingly, through the lens of quantum dynamics, we find that rotating the modulated field from parallel towards perpendicular to the projection axis induces an eigenstate transition between the diagonal and the constrained MBL phases. Remarkably, the growth of the entanglement entropy in constrained MBL follows a double-logarithmic form, whereas it changes to a power law in the diagonal limit. Although the diagonal MBL steered by a strong modulation along the projection direction can be understood by extending the phenomenology of local integrals of motion, a thorough analysis of the constrained MBL calls for the new ingredients. As a preliminary first step, we unveil the significance of confined nonlocal effects in the integrals of motion of the constrained MBL phase, which potentially challenges the established framework of the unconstrained MBL. Since the quasiperiodic modulation has been achievable in cold-atom laboratories, the constrained and diagonal MBL regimes, as well as the eigenstate transition between them, should be within reach of the ongoing Rydberg experiments.Comment: 9 pages, 5 figure

Lieb-Robinson Bounds, Out-of-Time-Order Commutators, and Lightcone Structures of Unconventional Many-Body Localization in Constrained Quantum Systems

Study how quantum information propagates through the spacetime manifold may provide a useful means of identifying, distinguishing, and classifying the unconventional phases of matter fertilized by many-body effects in strongly interacting systems in and out of equilibrium. Via a fuller characterization of the key aspects regarding the descendent novel dynamical processes, we performed such an analysis on the constrained many-body-localized phase -- a newly-discovered fully localized state in the infinite-interaction limit -- in the quasirandom Rydberg-blockaded spin chains using the thermal out-of-time-ordered commutators (OTOCs). The calculated OTOC lightcone contours predict a new and hitherto unknown Lieb-Robinson bound for the constrained many-body localization, which is qualitatively different from that of the conventional unconstrained many-body Anderson insulators normally arising in the weak-interaction limit. Our combined numerical and analytical investigation thus suggests that the constrained many-body localization is a distinct dynamical phase of matter in constrained quantum systems whose underlying mechanism of nonergodicity is beyond the existing phenomenology of quasilocal integrals of motion. Further, it also consolidates the hierarchy of unconventional quantum dynamics that encompasses constrained, unconstrained, and diagonal many-body-localized states.Comment: 6 pages, 5 figures (main) and 18 pages (supp