Single photon sources based on quantum dots produce indistinguishable photons on demand — the fundamental resource for photonic quantum computing and quantum communication. Lithium tantalate waveguides provide fast electro-optic modulation — the ability to route photons at GHz speeds by switching refractive indices with applied voltage. Combining them on a single chip would create a platform where photons are generated, routed, and processed in one integrated circuit.
Xiong et al. (arXiv:2603.12643) demonstrate this hybrid integration using micro-transfer printing. Indium arsenide quantum dots in gallium arsenide waveguides are printed onto lithium tantalate photonic circuits with alignment-tolerant coupling. The coupling works through tapered waveguide transitions: the GaAs waveguide narrows to a point while the LiTaO₃ waveguide widens from a point, and the evanescent field transfers smoothly between them. The taper design makes the coupling robust to the positioning errors inherent in micro-transfer printing.
At cryogenic temperatures, the quantum dot emits single photons into the GaAs waveguide, which couples into the LiTaO₃ circuit, where electro-optic switches route successive photons to different outputs deterministically. The single-photon nature is preserved through the coupling — the photon statistics measured at the output show antibunching consistent with a single quantum emitter.
This is the first demonstration of high-speed single-photon routing on a hybrid quantum dot–lithium tantalate platform. Previous quantum photonic circuits used either silicon nitride (passive, no fast switching) or lithium niobate (fast switching but harder to integrate with quantum dots). Lithium tantalate offers comparable electro-optic coefficients to lithium niobate with better fabrication compatibility for the hybrid integration approach.