Chip-Scale\nSingle-Beam Atomic Magnetometer Enabled\nby Spin-Selective Interference Meta-Optics

Emerging atomic magnetometers (AMs)\nare among the most\nadvanced\nsensors for detecting and characterizing magnetic fields. Recently,\nthere has been growing interest in the miniaturization and integration\nof AMs due to the urgent demand for portability and compactness in\nvarious fields such as biomagnetism imaging. While conventional AMs\nrequire a bulky setup of optical devices for the pumping and optical\nreadout of atomic spin, here, a novel chip-scale single-beam AM scheme\nis proposed by leveraging extreme transmissive circular polarization\ndichroism (TCPD) and geometric phase manipulation of spin-selective\ninterference meta-optics. This is achieved through silicon-based metasurfaces\nthat enable the realization of arbitrary-to-circular polarization\nconversion and wavefront modulation within a monolithic chip at Rb\nD1 transition wavelength (λ = 795 nm). Two spin-selective interference\nmetasurfaces, i.e., meta-circular-polarizer (MCP) and meta-circular-polarizer-lens\n(MCPL), are fabricated and characterized, with a measured TCPD of\n0.68 for the MCP as well as focusing efficiency and TCPD of around\n70.67% and 0.69 for the MCPL, respectively. As a proof of concept,\na 4 × 4 × 4 mm<sup>3</sup> Rb vapor cell is combined with\nour metasurface to construct a miniaturized single-beam AM. The sensitivity\nof our compact metasurface-based system is about 15 fT/Hz<sup>1/2</sup>, with a dynamic range near zero-field of ± 2.2 nT. We envision\nthat this work could facilitate the development of burgeoning chip-scale\nquantum sensors, which hold great potential for high-spatial-resolution\nbiomagnetic imaging, on-chip nuclear magnetic resonance, and so forth.