Non-Hermitian Quantum Physics

Abstract: Beyond-hermitian physics has recently attracted a great deal of attention due to remarkable advances in experimental techniques and theoretical methods in AMO, condensed matter and nonequilibrium statistical physics. Complete knowledge about quantum jumps allows a description of quantum dynamics at the single-trajectory level. A subclass thereof without quantum jumps can be described by a non-hermitian Hamiltonian. Here, symmetry, topology and many-body effects are fundamentally altered. Importantly, transposition and complex conjugation, which are equivalent in hermitian physics, become inequivalent, leading to proliferation of new topological phases and symmetry classes. In random matrix theory, transposition symmetry leads to two new universality classes of level-spacing statistics other than the Ginibre ensemble. In many-body physics, non-hermiticity leads to the dynamical sign reversal of magnetism in dissipative Hubbard models, violation of the g-theorem in the Kondo problem, and quantum phase transitions without gap closing. In the lecture, I will provide an overview on the fundamentals and new frontiers about beyond-Hermitian quantum physics.

About the speaker: Masahito Ueda is a Professor in the Physics department at the University of Tokyo and Leader of the RIKEN Center for emergent matter science, as well as director of the Ueda Macroscopic Quantum Control Project, ERATO, from Japan Science and Technology Agency (JST). He received numerous awards, including the JSPS Prize from the Japan Society for the Promotion of Science and the Nishina Memorial Prize. His broad research interests span ultracold atoms (spinor-dipolar Bose-Einstein condensates, topological excitations, symmetry breaking, and BCS-BEC crossover), Quantum information (spin squeezing and information thermodynamics), Information Thermodynamics, Measurement theory, and Mesoscopic physics. Reference: Y. Ashida, Z. Gong, and M. Ueda, Adv. Phys. 69, 249 (2021).