Efficient Cholesteric Liquid Crystal Waveguide Polarizing Splitters for High‐Sensitivity Chip‐Scale Atomic Magnetometry

High‐sensitivity spin‐exchange relaxation‐free atomic magnetometers represent the frontier of quantum sensing, yet conventional bulky polarizing beam splitters (PBSs) remain a critical barrier to chip‐scale integration. Here, we report an integrated polarimetry architecture based on a cholesteric liquid crystal (CLC) waveguide polarization splitter (WPS). By leveraging the synergy between the Bragg‐selective reflection of patterned CLCs and total‐internal‐reflection‐induced helicity inversion, this approach enables the efficient spatial decoupling and parallel emission of orthogonal circular polarizations within an ultrathin profile. We developed two application‐oriented WPS designs: a monolithic architecture optimized for high efficiency (90%) and architectural simplicity, and a cascaded architecture tailored for superior extinction ratios (141/134) and geometric symmetry. Experimental results show that the monolithic WPS reduces the optical system volume to merely 3.3% of traditional PBS‐based setups while achieving a magnetic sensitivity of 13 fT/Hz 1/2 . This sensitivity is on par with traditional bulky polarimetry schemes and surpasses existing state‐of‐the‐art integrated solutions. Furthermore, the CLC‐WPS is compatible with established liquid crystal manufacturing processes, offering a scalable and cost‐effective fabrication route obviating the need for expensive nanolithography. This work paves the way for mass‐producible, high‐performance quantum sensors, with broad implications for high‐resolution biomagnetic imaging systems.