Speaker's Brief Introduction：Io-Chun Hoi was born in Macau, China. He received B.S. and Ph.D. from the Electro-Physics Department at National Chiao Tung University, Taiwan, and from the Department of Microtechnology and Nanoscience at Chalmers University of Technology, Sweden, in 2007 and 2013, respectively. He conducted his postdoctoral research with Prof. John Martinis, Nobel Laureate in Physics 2025, at the University of California, Santa Barbara, U.S.A., from 2013 to 2015. He was an assistant professor and later an associate professor at National Tsing Hua University, Taiwan, from 2015 to 2021. He joined the City University of Hong Kong as a Tenured Associate Professor in 2021. He is the author or co-author of over 30 publications, including 1 first-authored Nature Physics, 3 first-authored Physical Review Letters, and 3 corresponding-authored Physical Review Letters. His research has garnered more than 4,600 citations, according to Google Scholar.
Abstract: In this talk, I will address recent advances in waveguide quantum electrodynamics with superconducting artificial atoms and spin ensembles.
In the first set of experiments, we demonstrate two methods, both using just a single artificial atom, that enable dynamic control over the velocities of microwave light. Our methods are based on two distinct mechanisms that harness the balance between the radiative and non-radiative decay rates of a superconducting artificial atom in front of a mirror. In the first method, we tune the radiative decay of the atom using interference effects due to the mirror; in the second method, we pump the atom to control its non-radiative decay through the Autler-Townes effect. When half of the radiative decay rate exceeds the non-radiative decay rate, we observe a positive group delay; conversely, the dominance of the non-radiative decay rate results in a negative group delay.
In the second set of experiments, we investigate the use of photonic crystal waveguides as a novel platform for studying light-matter interactions manifested through emitter-photon bound states. While such physics has been well-explored with quantum dots, cold atoms, and superconducting qubits, its application in magnonic systems remains largely uncharted. We present the first experimental demonstration of bound-state magnonics by coupling yttrium iron garnet spheres to a microwave photonic crystal waveguide. At room temperature, we achieve magnon-photon bound states characterized by tunable localization, power-dependent interaction modulation via microwave pumping, and long-range magnon-magnon interactions facilitated by overlapping bound states.