Atomic Spin Detection Method Based on Spin‐Selective Beam‐Splitting Metasurface

Abstract The current polarization differential detection method used for atomic co‐magnetometers and other atomic sensors usually depends on the beam splitting plane at 45° from the incident light, so the beam splitter needs a certain thickness and a second optical path perpendicular to the original optical axis for detection, which restricts the integration degree of the beam splitter and photodetectors on the probe optical path. To address this issue, a new spin‐selective beam‐splitting metasurface‐based technique for atomic spin detection is proposed in this study, which utilizes a silicon nitride (SiN) metasurface for chiral beam‐splitting detection. The experimental results show that the 2.8 × 2.8 mm fabricated metasurface supports the beam splitting focusing of the left and right circular partial incident light with a distance up to 1.340 mm. It has a remarkable ability to detect optical rotation angles, achieving an angular measurement sensitivity of 3.0526 × 10⁻⁵ rad at 70 kHz. Compared with the traditional beam splitter, the probe's optical path volume can be reduced by at least 80%. This method can enhance the integration of atomic sensors and provide a novel approach for the development of atom sensors on chips.