Metrologically enhanced multi-atom entangled states

With the advent of the second quantum revolution, the advances in quantum theory have given rise to a suite of emerging quantum technologies. As a representative branch in this field, quantum metrology leverages quantum entanglement to achieve precise measurements that overcome classical limits, rendering it a pivotal avenue for realizing unprecedented measurement accuracy. Accordingly, extensive theoretical and experimental investigations have been conducted on quantum states endowed with metrological enhancement features, and the preparation and application of such states have been demonstrated across diverse physical systems. Focusing on their properties and preparation, this paper describes some typical multi-atom entangled states that exhibit metrological enhancement, including spin-squeezed states, Greenberger—Horne—Zeilinger (GHZ) states, GHZ-like states, Dicke states, and spin-nematic squeezed states. Prospects for future developments in this research field are also assessed.