Direct Observation of Stability Enhancement in a Spin-squeezed Strontium Optical Lattice Clock Comparison

Current state-of-the-art atomic clocks are reaching the fundamental precision limit set by the quantum projection noise (QPN) of uncorrelated atoms. The incorporation of spin-squeezing in atomic samples enables clocks to perform below the QPN limit. Here, we present the recent experimental progress of our spin-squeezed strontium optical lattice clock. We generate spin-squeezed states of atoms via cavity QED-based quantum nondemolition measurements. In addition, a movable optical lattice enables spin squeezing of two spatially separate atomic sub-ensembles that are independently addressed by the cavity. In a direct, synchronous clock comparison between the two spin-squeezed atomic sub-ensembles, we measure a clock stability enhancement of 2.0(3) dB beyond the QPN-limit and reach a measurement precision at the 10^-17 level [1].

[1] Robinson, J.M., et al. “Direct comparison of two spin squeezed optical clocks below the quantum projection noise limit.” arXiv preprint arXiv:2211.08621 (2022).