Eta-Pairing in Hubbard Models: From Spectrum Generating Algebras to Quantum Many-Body Scars

Abstract

We revisit the $\eta$-pairing states in Hubbard models and explore their connections to quantum many-body scars to discover a universal scars mechanism. $\eta$-pairing occurs due to an algebraic structure known as a Spectrum Generating Algebra (SGA), giving rise to equally spaced towers of eigenstates in the spectrum. We generalize the original $\eta$-pairing construction and show that several Hubbard-like models on arbitrary graphs exhibit SGAs, including ones with disorder and spin-orbit coupling. We further define a Restricted Spectrum Generating Algebra (RSGA) and give examples of perturbations to the Hubbard-like models that preserve an equally spaced tower of the original model as eigenstates. The states of the surviving tower exhibit a sub-thermal entanglement entropy, and we analytically obtain parameter regimes for which they lie in the bulk of the spectrum, showing that they are exact quantum many-body scars. The RSGA framework also explains the equally spaced towers of eigenstates in several well-known models of quantum scars, including the AKLT model.

13 pages v2: typos corrected, references added

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Cited by in corpus (8)

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• Quantum Many-Body Scars in Spin-1 Kitaev Chains
• Quantum Many-Body Scars from Einstein-Podolsky-Rosen States in Bilayer Systems
• Quantum many-body scars of spinless fermions with density-assisted hopping in higher dimensions
• Steady off-diagonal long-range order state in a half-filled dimerized Hubbard chain induced by a resonant pulsed field