A Strontium Optical Lattice Clock System with Integrated Photonics

We report on implementing a strontium optical lattice clock system with integrated-photonics devices, which streamline laser-beam emission for laser cooling and laser-frequency stabilization. We realize magneto-optical trapping of ⁸⁸Sr and ⁸⁷Sr atoms and laser cooling to microkelvin temperature without free-space optics. With metasurface optics co-integrated on 75 mm fused silica wafers, we generate the complex, twelve-beam configuration for strontium two-stage laser cooling on the broad-line 461 nm and narrow-line 689 nm transitions. The metasurface-optics system with input from polarization-maintaining fibers provides nearly arbitrary control over laser-beam pointing, divergence, and polarization. Moreover, this monolithic system is assembled without active alignment, and it operates without maintenance or degradation for over a year. To frequency stabilize and linewidth narrow the lasers for the strontium lattice clock system, we use a frequency-comb system based on integrated nonlinear nanophotonic waveguides, which provide access to output light across the 650 nm to 2500 nm range. We phase-lock the repetition frequency of a 1550 nm erbium modelocked laser to an ultrastable reference laser, and by group-velocity dispersion engineering, we generate supercontinuum at 689 nm, 698 nm, 780 nm, 813 nm, and 922 nm to phase lock the red MOT laser, clock laser, modelocked laser carrier-envelope offset frequency, the lattice laser, and the blue MOT laser, respectively. We combine this integrated-photonics infrastructure with a vacuum chamber, laser-heated Sr vapor source, ion pump, and magnetic-field coils into a compact assembly of approximately 1 L volume. We explore the operation of this strontium optical lattice clock system, including blue MOT trapping of ⁸⁸Sr and ⁸⁷Sr atoms directly from the heated Sr source. Furthermore, we have demonstrated red MOT trapping of 88Sr atoms at microkelvin temperature and optical lattice trapping with ~300 ms lifetime. Experiments to observe the Sr clock transition at 698 nm are ongoing. This integrated photonics system offers robust and manufacturable functionalities for quantum sensing and quantum information applications.