Tunable coherent microwave beam splitter and combiner at the single-photon level
Y.-H. Huang, Kaun-Chun Hsieh, F. Aziz, Zhengqi Niu, P. Y. Wen, Y. -T. Cheng, Yi-Chien Tsai, Jeng‐Chung Chen, Xin Wang, Anton Frisk Kockum, Z.-R. Lin, Y. -H. Lin, I.-C. Hoi · Applied Physics Letters · 2025
A beam splitter is a key component used to direct and combine light paths in various optical and microwave systems. It plays a crucial role in devices like interferometers, such as the Mach–Zehnder and Hong–Ou–Mandel setups, where it splits light into different paths for interference measurements. These measurements are vital for precise phase and coherence testing in both classical and quantum optical experiments. In this work, we present a nonlinear beam splitter and beam combiner utilizing a frequency-tunable superconducting artificial atom in a one-dimensional open waveguide. Probed with coherent states at the single-photon level (average photon number ⟨N⟩ ≪1), this device demonstrates highly tunable transparency, ranging from near unity to complete reflection. Additionally, the beam combiner can merge two coherent beams, generating interference fringes as the relative phase between them varies.