Diabolical points in coupled active cavities with quantum emitters

In single microdisks, embedded active emitters intrinsically affect the cavity modes of the microdisks, resulting in trivial symmetric backscattering and low controllability. Here we demonstrate macroscopic control of the backscattering direction by optimizing the cavity size. The signature of the positive and negative backscattering directions in each single microdisk is confirmed with two strongly coupled microdisks. Furthermore, diabolical points are achieved at the resonance of the two microdisks, which agrees well with theoretical calculations considering the backscattering directions. Diabolical points in active optical structures pave the way for an implementation of quantum information processing with geometric phase in quantum photonic networks. Diabolically good control over quantum emitters A system of tiny coupled disks developed by researchers in China and Scotland could provide control over the emission of individual photons for quantum computing. Single-photon emitters are required for passing information in quantum photonic networks, but it is very difficult to control the direction that photons are emitted or to stop neighboring emitters from interfering. Xiulai Xu at the Chinese Academy of Sciences and co-workers fabricated pairs of 1-micrometer-radius disks, surrounded by even smaller particles called quantum dots. By exciting the quantum dots with a laser, the researchers set up so-called diabolical points in the coupled microdisks. These points allow control over the backscattering of light, as a function of the distance between disks. The study not only provides a new platform for quantum information processing but could also enable controllable directional lasers.