Electronically programmable photonic molecule

Physical systems with discrete energy levels are ubiquitous in nature and acre fundamental building blocks of quantum technology. Realizing controllable artificial atom- and molecule-like systems for light would enable coherent and dynamic control of the frequency, amplitude and phase of photons^1–5. In this work, we demonstrate a ‘photonic molecule’ with two distinct energy levels using coupled lithium niobate microring resonators and control it by external microwave excitation. We show that the frequency and phase of light can be precisely controlled by programmed microwave signals, using concepts of canonical two-level systems including Autler–Townes splitting, Stark shift, Rabi oscillation and Ramsey interference. Through such coherent control, we show on-demand optical storage and retrieval by reconfiguring the photonic molecule into a bright–dark mode pair. These results of dynamic control of light in a programmable and scalable electro-optic system open doors to applications in microwave signal processing⁶, quantum photonic gates in the frequency domain⁷ and exploring concepts in optical computing⁸ and topological physics^3,9.