A powerful framework allows scientists to understand and classify joint quantum measurements—procedures essential for many quantum technologies.

Two key, yet enigmatic, aspects of quantum physics are entanglement and the act of measuring a quantum system. These elements combine in unique ways in so-called joint measurements, where multiple systems are simultaneously measured in a way that accounts for their entanglement. Joint measurements are valuable because they can extract hidden information about the combined state of the systems. Remarkably, the outcome of a joint measurement can be replicated even if the systems are kept far apart, which has many practical benefits. Such “localization” procedures require local operations to be performed on each system and some extra entanglement to be shared beforehand. Now Jef Pauwels and colleagues at the University of Geneva have investigated how much of this shared entanglement is needed to localize a given joint measurement [1].