From tunnels to towers: Quantum scars from Lie algebras and q-deformed Lie algebras

Journal Article · 02 December 2020 · Physical Review Research

DOI: https://doi.org/10.1103/physrevresearch.2.043305 · OSTI ID:1730971

O'Dea, Nicholas ^[1]; Burnell, Fiona ^[2]; Chandran, Anushya ^[3]; Khemani, Vedika ^[1]

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1. Stanford Univ., CA (United States)
2. Univ. of Minnesota, Minneapolis, MN (United States)
3. Boston Univ., MA (United States)

We present a general symmetry-based framework for obtaining many-body Hamiltonians with scarred eigenstates that do not obey the eigenstate thermalization hypothesis. Our models are derived from parent Hamiltonians with a non-Abelian (or q-deformed) symmetry, whose eigenspectra are organized as degenerate multiplets that transform as irreducible representations of the symmetry (`tunnels'). We show that large classes of perturbations break the symmetry, but in a manner that preserves a particular low-entanglement multiplet of states -- thereby giving generic, thermal spectra with a `shadow' of the broken symmetry in the form of scars. The generators of the Lie algebra furnish operators with `spectrum generating algebras' that can be used to lift the degeneracy of the scar states and promote them to equally spaced `towers'. Our framework applies to several known models with scars, but we also introduce new models with scars that transform as irreducible representations of symmetries such as SU(3) and q-deformed SU(2), significantly generalizing the types of systems known to harbor this phenomenon. Additionally, we present new examples of generalized AKLT models with scar states that do not transform in an irreducible representation of the relevant symmetry. These are derived from parent Hamiltonians with enhanced symmetries, and bring AKLT-like models into our framework.

• Research Organization: Stanford Univ., CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR); USDOE
• Grant/Contract Number: SC0021111; DMR-1752759; DMR-1928166; FA9550-20-1-0235
• OSTI ID: 1730971
• Alternate ID(s): OSTI ID: 1785237
• Journal Information: Physical Review Research, Vol. 2, Issue 4; ISSN 2643-1564
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English