| Neutral atom optical standards require the highest levels of laser precision to operate near the limit set by quantum fluctuations. We develop state-of-the-art ultra-stable laser systems to achieve a factor of 10 enhancement in clock measurement precision and additionally demonstrate optical linewidths below 50 mHz. The most stable of these lasers reaches its thermal noise floor of 1 × 10−16 fractional frequency instability, allowing the attainment of near quantum-noise-limited clock operation with single-clock instabilities of 3 × 10−16 at t . We utilize this high level of spectral resolution to operate a 87Sr optical lattice clock in a regime in which quantum collisions play a dominant role in the dynamics, enabling the study of quantum many-body physics. With a fractional level of precision of near 1 × 10 −16 at 1 s, we clearly resolve the signatures of many-body interactions. We find that the complicated interplay between the p wave-dominated elastic and inelastic interaction processes between lattice-trapped atoms leads to severe lineshape distortion, shifts, and loss of Ramsey fringe contrast. We additionally explore the theoretical prediction that these many-body interactions will modify the quantum fluctuations of the system and we find that in certain parameter regimes the quantum noise distribution exhibits a quadrature dependence. We further present technological advancements that will permit ultra-stable lasers to operate with reduced thermal noise, leading to a potential gain of an additional factor of 10 in stability. This indicates that laser fractional frequency instabilities of 1 × 10−17 are within experimental reach, as is a fully-quantum-limited regime of optical clock operation. |
