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/Hz1/2. 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.