University of Connecticut Perturbative Theory Predicts Plateau Height & Timescale
A perturbative theory developed by C. L. Sriram and Lea F. Santos at the University of Connecticut, and Soumya Kanti Pal at the Tata Institute of Fundamental Research, now provides analytical expressions for both the height and timescale of how long it takes for strongly interacting quantum systems to approach equilibrium, a calculation previously beyond reach. Researchers found that nearly conserved quantities fragment the system’s quantum behavior, leading to a two-stage equilibration process with long-lived prethermal plateaus. Unlike conventional eigenstate thermalization hypothesis, the team’s fragmented eigenstate thermalization hypothesis (fETH) obeys a symmetry-imposed selection rule that restricts which system sizes can be compared. This band-resolved description also explains ensemble inequivalence without invoking equilibrium phase transitions, offering a new perspective on statistical mechanics for systems exhibiting Hilbert-space fragmentation. Long-Range Interactions and Hilbert Space Fragmentation The structure of quantum chaos is being clarified by discoveries revealing how long-range interactions fundamentally alter the path to thermal equilibrium. Research led by C. L. Sriram at the University of Connecticut, in collaboration with Soumya Kanti Pal of the Tata Institute of Fundamental Research and Lea F. Santos at the University of Connecticut, demonstrates that systems exhibiting strong, long-range interactions do not simply scramble towards disorder as previously understood, but instead navigate a fragmented quantum landscape. The team’s work, dated July 16, 2026, details how these interactions split the system’s quantum states into distinct energy bands, dramatically slowing the approach to equilibrium. This fragmentation is not a roadblock to thermalization; instead, the study reveals that finite-size scaling in the team’s fragmented eigenstate thermalization hypothesis (fETH) obeys a symmetry-imposed selection rule that restricts which system s
