Record Precision Achieved in Direct Comparison of Spin-Squeezed Optical Lattice Clocks.

Researchers have demonstrated the first direct observations of an optical-lattice clock operating below the classical quantum projection noise (QPN) limit, averaging down to a measurement precision level of 10−17. By entangling the atomic sample, the researchers were able to reduce the QPN limit and improve the frequency stability of optical lattice clocks, which can be used for practical applications such as GPS and exploring fundamental physics. This represents a major step toward improving state-of-the-art optical lattice clocks through spin squeezing.