Approaching Optimal Light Evolution at Adiabaticity Control Limit in Inverse-Designed Waveguides

Controlling state evolution via adiabaticity has attracted significant interest for its vital role in quantum and photonic applications. However, attaining the adiabaticity control limit (ACL)-defined as the shortest possible duration with minimal mode crosstalk during evolution-remains a significant challenge. In this Letter, we address this issue by introducing an inverse adiabaticity control strategy, where the tolerable crosstalk serves as a control parameter. Taking the stimulated raman adiabatic passage as an example, we demonstrate the principle of inverse adiabaticity control and determine the map of optimal solution under various parameter constraints. The effectiveness and superiority of the inverse design strategy are experimentally demonstrated in silicon photonic waveguides. Crucially, we show that ACL solutions can achieve both the fastest and most robust evolution simultaneously, overcoming the usual tradeoff in conventional forward-designed structures and meeting key needs for photonic and quantum computing devices. The inverse control method offers a universal strategy that may be applicable across a wide range of physical settings.