Spin squeezing with Rydberg interactions in a neutral-atom optical-clock platform*

In the past five years, tweezer-loaded arrays of neutral strontium atoms have emerged as a promising system for explorations of quantum metrology in an optical clock platform, as they have demonstrated competitive coherence times and precision. Here, we present spin squeezing generated with Rydberg interactions in an array of neutral strontium atoms and observe nearly 4dB of metrological gain. Additionally, we perform a synchronous optical-frequency comparison between two ensembles of atoms and realize a stability that is 1.94(1) dB better than the standard quantum limit (SQL) and reaches the 10^-17-level of fractional-frequency precision in a half-hour measurement. We also discuss limitations to the squeezing protocol, as well as promising modifications which might allow for further improvements in metrological gain. While many challenges remain, this work represents an important step in building up the available tools for quantum metrology with optical clocks, and developing an understanding of when entangled states might provide a practical advantage for future applications.