Spin-squeezed strontium optical lattice clock comparison at the 10^-17 level

Synchronous comparisons between optical atomic clocks have enabled unprecedentedly precise probes of fundamental physics, from the underlying symmetries of nature to millimeter-scale resolution of the gravitational redshift [1, 2]. Such comparisons, however, are approaching the fundamental limit of precision set by the spin statistics of uncorrelated particles, known as quantum projection noise (QPN) [3]. By generating entanglement, in the form of spin squeezing, we can leverage ensemble-wide correlations to circumvent this QPN limit. We have constructed a hybrid platform with a strontium optical lattice clock complemented with an in-vacuum high-finesse cavity for state preparation and readout. By utilizing a conveyor belt lattice, we can shuffle distinct sub-regions of the atomic cloud in and out of the cavity to prepare two independent spin-squeezed ensembles. We perform a self-synchronous comparison between the two ensembles to observe spin squeezing-enhanced stability that averages down to the 10^-17 level [4]. We will report next steps towards entanglement-enhanced measurements in competitive optical clock performance.



1. C. Sanner et al., Nature 567, 204-208 (2019)

2. T. Bothwell et al., Nature 602, 420-424 (2022)

3. E. Oelker et al., Nature Photonics 13, 714-719 (2019)

4. J. M. Robinson et al., Nature Physics, 1-6 (2024).