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Welcome to a research seminar by Dr. Kang Yang from Freie Universität Berlin!

Host: KryÅ¡tof Kolář (Quantum Dynamics group)

Title: Engineering non-Abelian Berry curvatures via dissipation

Abstract: 

Geometric phases and Berry curvatures are particular features of quantum states following adiabatic evolutions. They lead to rich physical phenomena in transports, topological phases and correlated states in metals. Many of these interesting properties can also arise in photons transmitting in periodic media. There, dissipation is inevitable and gives rise to effective non-Hermitian evolutions. 

In this presentation, I will demonstrate a new form of topological transition in parity-time symmetric systems. Upon increasing loss and gain, the eigenstates of these systems can spontaneously break the symmetry. The non-Abelian Berry curvatures of the eigenstates in the symmetry preserving regime and those in the symmetry breaking regime quantise in qualitatively different forms. I will show that this transition is described by a new mechanism—topological duality, where the Chern numbers in the spontaneous-symmetry-breaking regime must equal the Euler numbers in the symmetry-preserving regime. These results demonstrate that loss and gain can engineer the non-Abelian gauge structures of physical states and provide new ideas to prepare topological phenomena.