Nonthermal eigenstates and slow relaxation in quantum Fredkin spin chains

Causer, Luke; Bañuls, Mari Carmen; Garrahan, Juan P.

Abstract

We study the dynamics and thermalization of the Fredkin spin chain, a system with local three-body interactions, particle conservation, and explicit kinetic constraints. We consider deformations away from its stochastic point in order to tune between regimes where kinetic energy dominates and those where potential energy does. By means of exact diagonalization, perturbation theory, and variational matrix product states, we show there is a sudden change of behavior in the dynamics that occurs, from one of fast thermalization to one of slow metastable (prethermal) dynamics near the stochastic point. This change in relaxation is connected to the emergence of additional kinetic constraints, which lead to the fragmentation of Hilbert space in the limit of a large potential energy. We also show that this change can lead to thermalization being evaded for special initial conditions because of nonthermal eigenstates (akin to quantum many-body scars). We provide clear evidence for the existence of these nonthermal states for large system sizes even when far from the large-potential-energy limit, and explain their connection to the emergent kinetic constraints.

Citation

Causer, L., Bañuls, M. C., & Garrahan, J. P. (2024). Nonthermal eigenstates and slow relaxation in quantum Fredkin spin chains. Physical Review B, 110(13), Article 134322. https://doi.org/10.1103/physrevb.110.134322

• Journal Article Type: Article
• Acceptance Date: Oct 9, 2024
• Online Publication Date: Oct 30, 2024
• Publication Date: Oct 1, 2024
• Deposit Date: Oct 31, 2024
• Publicly Available Date: Oct 31, 2024
• Journal: Physical Review B
• Print ISSN: 2469-9950
• Electronic ISSN: 2469-9969
• Publisher: American Physical Society
• Peer Reviewed: Peer Reviewed
• Volume: 110
• Issue: 13
• Article Number: 134322
• DOI: https://doi.org/10.1103/physrevb.110.134322
• Keywords: Eigenstate thermalization; Entanglement entropy; Quantum scars; 1-dimensional spin chains; Exact diagonalization; Tensor network methods
• Public URL: https://nottingham-repository.worktribe.com/output/41160389
• Publisher URL: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.110.134322