The dichotomy of localization versus delocalization is a historic topic central to quantum and condensed matter physics. We discover a new delocalization mechanism attributed to a residue imaginary (part of) velocity $\operatorname{Im}(v)$, feasible for ground states or low-temperature states of non-Hermitian quantum systems under periodic boundary conditions. We numerically demonstrate such delocalization with correlation, entanglement, and generalizability to finite temperatures and interactions. Interestingly, a disorder field contributing to $\operatorname{Im}(v)$ may allow strong-disorder-limit delocalization when $\operatorname{Im}(v)$ prevails over the Anderson localization; there, the delocalization takes on a many-body nature, in contrast to the conventional formalism of extended single-particle wavefunctions in weak disorder or Hermitian systems. Thus, the nontrivial physics of $\operatorname{Im}(v)$ significantly enriches our understanding of delocalization and breeds useful applications, e.g., in quantum adiabatic processes.

Prof. Yi Zhang is a theoretical condensed matter physicist. He obtained his undergraduate degree at Fudan University and his Ph.D. at UC Berkeley under advisor Prof. Ashvin Vishwanath. Afterward, Dr. Yi Zhang joined Stanford University as a SITP postdoctoral fellow and later Cornell University as a Bethe fellow. Then, he joined the International Center for Quantum Materials at Peking University. Yi Zhang is interested in emergent phenomena and novel approaches in quantum materials, systems, and algorithms, including machine-learning methods and non-Hermitian perspectives for characterizations and analysis of quantum many-body systems.