Efficient broadband polarization retarder via shortcuts to adiabaticity

The use of two-level atomic systems in quantum optics allows for the design of highly efficient and broadband achromatic retarders through the application of adiabatic passage and composite pulse techniques. In this work, we propose shortcuts to adiabaticity to improve broadband polarization retarders with shorter lengths. We achieve this by inversely engineering the relative refractive indices and further optimizing them with respect to the perturbation of input wavelength. Our results are compared with adiabatic and composite protocols, demonstrating that our method provides the advantage of integrating efficiency and robustness.