Fault-Tolerant Directional Couplers for State Manipulation in Silicon Photonic-Integrated Circuits

Photonic integrated circuits play a central role in current and future applications such as communications, sensing, ranging, and information processing. Photonic quantum computing will also likely require an integrated optics architecture for improved stability, scalability, and performance. Fault-tolerant quantum computing mandates very accurate and robust quantum gates. In this work, we demonstrate high-fidelity directional couplers for single-qubit gates in photonic integrated waveguides, utilizing a novel scheme of detuning-modulated composite segments. Specific designs for reduced sensitivity to wavelength variations and real-world geometrical fabrication errors in waveguides width and depth are presented. Enhanced wavelength tolerance is demonstrated experimentally. The concept shows great promise for scaling high fidelity gates as part of integrated quantum optics architectures.