Open systems with loss or gain, described by effective non-Hermitian Hamiltonians, have attracted great attention in recent years. Such systems in general have complex energies and nonorthogonal eigenstates, and their degeneracies are known as exceptional points. The complex energies near an exceptional point form a Riemann manifold, whose topology enables a new control method and has found applications in energy transport and mode switch. In this talk, I will present our recent work on dynamical control of a non-Hermitian superconducting qubit. By varying the Hamiltonian parameters in real time to encircle an exceptional point, we observe that the qubit initialized at one eigenstate is transported to another eigenstate. We further study the chiral geometric phase associated with quantum coherent state transport on the Riemann manifold. In addition, I will discuss non-Hermitian physics based on Liouvillian superoperators, which goes beyond the existing Hamiltonian formalism and allows us to observe decoherence-induced exceptional points.
Weijian Chen is a Postdoctoral Research Associate at Washington University in St. Louis, where he gained his PhD and Masters. His research interests include Superconducting circuits, Photonics Quantum sensing and Non-Hermitian physics.