Counterdiabatic mode-evolution based coupled-waveguide devices

The goal in designing mode-evolution based devices is to realise short and high-fidelity components. The counterdiabatic protocol in coherent quantum state control can be used to cancel unwanted coupling between adiabatic modes in mode evolution but is not directly realisable in the coupled-waveguide system. By finding alternative coupled-mode equations that links to the same interaction picture dynamical equation as the counterdiabatic protocol via unitary transformations, we have derived a universal formalism for the design of short and high-fidelity mode-evolution based coupled-waveguide devices. Starting from a traditional adiabatic device design, the counterdiabatic protocol leads to a high-fidelity device, with its evolution following the adiabatic modes exactly even when the adiabatic condition is violated. Tolerance analysis shows that the counteradiabatic devices combine the advantages of adiabatic and resonant devices. The formalism is used to design asymmetric waveguide couplers.