Onsager's Scars in Disordered Spin Chains

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Statistical Physics

Background:

• Quantum many-body scars are rare, non-thermalizing states in quantum systems.
• Disorder typically drives quantum systems towards thermalization.
• The eigenstate thermalization hypothesis (ETH) predicts thermalization for generic highly excited states.

Purpose of the Study:

• To propose and construct novel nonintegrable quantum spin chains exhibiting quantum many-body scars.
• To investigate the impact of disorder on quantum many-body scars.
• To explore the properties and dynamics of these scarred states, particularly their entanglement and thermalization behavior.

Main Methods:

• Construction of scarred models using Onsager symmetry for arbitrary spin quantum number S.
• Classification of scar states into coherent states and one-magnon scar states.
• Analysis of entanglement properties (area-law entanglement) and representation as matrix product states.
• Investigation of the dynamics of fidelity and entanglement entropy for various initial states.

Main Results:

• Demonstrated the existence of quantum many-body scars in nonintegrable quantum spin chains even with disorder.
• Identified two distinct types of scar states: Onsager-algebra coherent states and one-magnon scar states.
• Showcased that scar states possess area-law entanglement and violate the ETH.
• Observed that scar states exhibit periodic dynamics and remain localized in Hilbert space, preventing thermalization, unlike generic states.

Conclusions:

• The proposed models represent the first explicit examples of disordered quantum many-body scarred systems.
• These findings challenge the conventional understanding of disorder-induced thermalization in quantum systems.
• The existence of non-thermalizing scar states in disordered systems opens new avenues for exploring quantum dynamics and novel quantum phases.