A scalable infrastructure for strontium optical clocks with integrated photonics

Abstract

Optical atomic clocks provide exceptionally accurate and precise signals for timekeeping and precision measurements, but they require high-power, free-space laser configurations that limit scalability. We introduce and explore a scalable infrastructure for strontium (Sr) optical-lattice clocks that incorporates co-design of atomic-beam slowing and a magneto-optical trap (MOT) from an effusion source, generation of complex, three-dimensional free-space laser configurations with a photonic integrated circuit (PIC) and metasurface (MS) optics, and laser stabilization to a frequency-comb supercontinuum generated with integrated nonlinear photonics. With these elements, we realize MOTs of all stable strontium isotopes ($^{84}$Sr, $^{86}$Sr, $^{87}$Sr, $^{88}$Sr) with populations commensurate with natural abundances, demonstrating precise beam control and robustness. Access to laser-cooled alkaline-earth atoms with scalable integrated photonics enables system engineering for optical clocks, quantum sensing, and quantum information, and our experiments demonstrate extensible technologies that advance toward a Sr optical clock largely free of bulk optics.

Figures (3)

• Figure 1: Scalable infrastructure for optical lattice clocks.(a) Our Sr system includes a commercial effusive oven, mechanical feed through atomic beam shutter, differential pumping tube, atom-photonic interface such as metasurface chips, science chamber, and Doppler slowing beam introduced through a heated sapphire window. (b) Illustration of a customizable arrangement of multifunctional metasurface optics for MOT beam generation (c) Monte Carlo simulations of laser cooled atom trajectories of the planar MOT beam geometry. (d) Image of a realized $4\times10^5$ atom $^{87}$Sr MOT.
• Figure 2: PIC–MS approach for MOT beam generation. (a) Waveguides on a PIC chip route 461nm and 689nm light to apodized meta-grating couplers, which vertically outcouple light to a wafer with MS optics for Sr MOT beam formation. (b) Material layer stack of the PIC–MS architecture. (c) Photograph of a fabricated PIC routing 461nm (broad-line) and 689nm (narrow-line) strontium MOT light. (d) Monte Carlo simulations of relative MOT loading rates versus fabrication imperfections in waveguide width and thickness. (e) Loss characterization of the PIC–MS system. Low-power propagation loss is measured with on-chip powers of $\sim$1 mW at 461nm and 689nm (red and blue circles). After illumination at high power, length-dependent loss increases significantly for the PIC (purple–blue) and the full PIC–MS system (purple), with optical powers of 50 mW and 150 mW, respectively.
• Figure 3: MS optics approach for MOT beam generation(a) Illustration of MOT beam generation with direct illumination of multifunctional metasurface optics fabricated on a common substrate with free space beams. (b) Photo of 461nm and 689nm MS optics fabricated on common substrate. Subpanels show elliptical dimensions of a 461 nm metasurface optics and an SEM image of constituent nanopillars (c) Propagation, expansion, and intersection of MS derived 461nm MOT beams viewed on a fluorescent plate at the plate is translated vertically above the MS wafer.