Spin squeezing in a programmable optical clock with Rydberg interactions*

In recent years, ever-improving optical lattice clocks have been complemented by a novel platform: Atom arrays assembled by individual optical tweezers. Together with Rydberg interactions, the control at the single-particle level makes atom arrays an ideal platform for studying how many-body interactions can be harnessed for quantum-enhanced measurements of time.

Here, we report on realizing spin-squeezing in a programmable strontium optical clock using Rydberg interactions. We assemble near defect-free arrays of up to 140 atoms in an optical lattice potential utilizing dynamic optical tweezers. To entangle the atoms and produce spin-squeezed states, we employ a Rydberg-dressing protocol where a laser off-resonantly couples the clock state to a high-lying Rydberg state. We characterize the improved sensitivity of spin-squeezed states in a Ramsey interferometer by comparing two or more sub-ensembles of the atom array. This directly reveals enhanced fractional frequency stability below the standard quantum limit at a fixed averaging time. Our work paves the way for utilizing the programmability of atom arrays in more complex protocols for quantum-enhanced metrology, such as non-Gaussian states and variational optimization.