Approaching the adiabatic infimum of topological pumps on thin-film lithium niobate waveguides.

Topological pumps reveal topological insights of adiabatic mode evolution, in which adiabaticity plays a crucial role. However, the adiabatic infimum, i.e., the possible shortest evolution duration of an adiabatic topological pumping process, has remained elusive. In this study, we report the approach of adiabatic infimum in topological pumps in photonic waveguides based on the lithium niobate-on-insulator (LNOI) platform. Besides the most common way to achieve adiabaticity by slowing down the evolution of the system, the adiabaticity of a topological pump is also contingent on an effective Berry connection between instant eigenstates, which can be controlled by the selection of specific pump loops. Specifically, we develop a strategy to identify a pump loop with a minimized effective Berry connection, corresponding to the adiabatic infimum of a topological pump. As such, it is experimentally demonstrated that topological pumps can happen even with rapid evolution speed, at which the conventional pump would completely fail. The adiabatic infimum accelerates the topological pumps from the constraints of slow evolution and facilitates the design of compact topological devices.