Quantum many-body scars (QMBS) constitute a new quantum dynamical regime in which rare "scarred" eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volume-law for a random bipartition, while scaling for a fine-tuned bipartition is sub-extensive. When internal symmetries are present, the construction leads to multiple, and even towers of rainbow scars revealed through distinctive non-thermal dynamics. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydberg-atom quantum simulator, leading to coherent oscillations distinct from the strictly sub-volume-law QMBS previously realized in the same system.

1 aLanglett, Christopher, M.1 aYang, Zhi-Cheng1 aWildeboer, Julia1 aGorshkov, Alexey, V.1 aIadecola, Thomas1 aXu, Shenglong uhttps://arxiv.org/abs/2107.0341601383nas a2200157 4500008004100000245005600041210005500097260001400152490000800166520093200174100002001106700001601126700002501142700002101167856003701188 2020 eng d00aHilbert-Space Fragmentation from Strict Confinement0 aHilbertSpace Fragmentation from Strict Confinement c5/22/20200 v1243 aWe study one-dimensional spin-1/2 models in which strict confinement of Ising domain walls leads to the fragmentation of Hilbert space into exponentially many disconnected subspaces. Whereas most of the previous works emphasize dipole moment conservation as an essential ingredient for such fragmentation, we instead require two commuting U(1) conserved quantities associated with the total domain-wall number and the total magnetization. The latter arises naturally from the confinement of domain walls. Remarkably, while some connected components of the Hilbert space thermalize, others are integrable by Bethe ansatz. We further demonstrate how this Hilbert-space fragmentation pattern arises perturbatively in the confining limit of Z2 gauge theory coupled to fermionic matter, leading to a hierarchy of time scales for motion of the fermions. This model can be realized experimentally in two complementary settings.

1 aYang, Zhi-Cheng1 aLiu, Fangli1 aGorshkov, Alexey, V.1 aIadecola, Thomas uhttps://arxiv.org/abs/1912.0430001427nas a2200157 4500008004100000245007300041210006900114260001400183520092900197100001601126700002001142700002401162700002101186700002501207856003701232 2020 eng d00aLocalization and criticality in antiblockaded 2D Rydberg atom arrays0 aLocalization and criticality in antiblockaded 2D Rydberg atom ar c12/7/20203 aControllable Rydberg atom arrays have provided new insights into fundamental properties of quantum matter both in and out of equilibrium. In this work, we study the effect of experimentally relevant positional disorder on Rydberg atoms trapped in a 2D square lattice under anti-blockade (facilitation) conditions. We show that the facilitation conditions lead the connectivity graph of a particular subspace of the full Hilbert space to form a 2D Lieb lattice, which features a singular flat band. Remarkably, we find three distinct regimes as the disorder strength is varied: a critical regime, a delocalized but nonergodic regime, and a regime with a disorder-induced flat band. The critical regime's existence depends crucially upon the singular flat band in our model, and is absent in any 1D array or ladder system. We propose to use quench dynamics to probe the three different regimes experimentally.

1 aLiu, Fangli1 aYang, Zhi-Cheng1 aBienias, Przemyslaw1 aIadecola, Thomas1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2012.03946