Optical atomic clock interrogation using an integrated spiral cavity laser

Abstract

Optical atomic clocks have demonstrated revolutionary advances in precision timekeeping, but their applicability to the real world is critically dependent on whether such clocks can operate outside the laboratory. Photonic integration offers one compelling solution to address the miniaturization and ruggedization needed to enable clock portability, but brings with it a new set of challenges in recreating the functionality of an optical clock using chip-scale building blocks. The clock laser used for atom interrogation is one particular point of uncertainty, as the performance of the meticulously engineered bulk-cavity-stabilized lasers would be exceptionally difficult to transfer to chip. Here we demonstrate that an integrated ultrahigh-quality-factor spiral cavity, when interfaced with a 1,348 nm seed laser, is able to reach a fractional frequency instability of 7.5 × 10⁻¹⁴ on chip. On frequency doubling the light to 674 nm, we use this laser to interrogate the narrow-linewidth transition of ⁸⁸Sr⁺ and showcase the operation of a Sr-ion clock with short-term instability averaging down as \(3.9\times 1{0}^{-14}/\sqrt{\tau }\) (τ, averaging time). Our demonstration of a high-performance optical atomic clock interrogated by an integrated spiral cavity laser opens the door for future advanced clock systems to be entirely constructed using lightweight, portable and mass-manufacturable integrated optics and electronics.