Researchers have experimentally demonstrated multi-parameter quantum metrology with an array of entangled atomic ensembles.[1][3] They split the spin-compressed atomic ensemble into three entangled parts, creating a sensor array with inter-sensor entanglement.[1][3] Using an optimal estimation protocol, they achieved significant improvements in measurement accuracy over the standard quantum limit in key tasks.[1][2] This method allows the simultaneous measurement of several physical parameters, such as the spatial distribution of the electromagnetic field, with higher accuracy.[3] Experiments with two and three groups showed improvements of several tenths of a decibel over classical methods.[2] Entanglement of atomic spins reduces measurement uncertainties and compensates for perturbations acting equally on all spins.[3] Applications include atomic clocks, gravimeters, and measurement of spatial variations in gravity.[3]