Quantum engineering for practical advantages in clocks

Precise quantum state engineering and many-body physics build the foundation for quantum system scaling to enhance measurement performance for atomic clocks. The use of many atoms reduces the quantum projection noise, while Hamiltonian engineering guards against systematic effects. Minute-long coherence in the optical domain has been achieved for tens of thousands of atoms. Quantum entanglement is also embedded in clock operation near the state of the art. Such precise control of light-matter interactions is fostering new capabilities for probing fundamental and emerging phenomena.