All-optical input-agnostic polarization transformer via experimental Kraus-map control

The polarization of light is utilized in many technologies throughout science and engineering. The ability to transform one state of polarization to another is a key enabling technology. Common polarization transformers are simple polarizers and polarization rotators. Simple polarizers change the intensity depending on the input state and can only output a fixed polarized state, while polarization rotators rotates the input Stokes vector in the 3D Stokes space. We experimentally demonstrate an all-optical input-agnostic polarization transformer (AI-APT), which transforms all input states of polarization to a particular state that can be polarized or partially polarized. The output state of polarization and intensity depends solely on setup parameters, and not on the input state, thereby the AI-APT functions differently from simple polarizers and polarization rotators. The AI-APT is completely passive, and thus can be used as a polarization controller or stabilizer for single photons and ultrafast pulses. To achieve this, we, for the first time, experimentally realize complete kinematic state controllability of an open single-qubit by Kraus maps put forth in Wu et al. (J Phys A 40:5681, 2007). The AI-APT may open a new frontier of partially polarized ultrafast optics.