Controlled unidirectional reflectionlessness by coupling strength in a non-Hermitian waveguide quantum electrodynamics system

Unidirectional reflectionlessness is investigated in a waveguide quantum electrodynamics system that consists of a cavity and a $\Lambda$-type three-level quantum dot coupled to a one-dimensional plasmonic waveguide. Analytical expressions of transmission and reflection coefficients are derived and discussed for both resonant and off-resonant couplings. By appropriately modulating the coupling strength, phase shift and Rabi frequency, unidirectional reflectionlessness is observed at the exceptional points. And unidirectional coherent perfect absorption is exhibited at the vicinity of exceptional point. These results might find applications in designing quantum devices of photons, such as optical switches and single-photon transistors.Comment: 11 pages, 7 figure

Nonreciprocal photon transport in indirectly coupled whispering-gallery mode resonators

We study the reflection and transmission properties of a system comprising two whispering-gallery mode resonators, each containing a Zeeman-split quantum dot and side-coupled to an optical fiber. Our results demonstrate that unidirectional reflection and transmission can be achieved by tuning the coupling strength between the resonators and the optical fiber. Furthermore, we establish a correspondence between quantum dot energy level resonance frequencies and the positions of low reflection (transmission) peaks at a phase shift of {\pi}. This research provides insights for the development of quantum optical devices like isolators, circulators, and routers.Comment: 9 pages, 6 figures, 47 reference