Quantum technologies, devices that can process, store, or detect information leveraging quantum mechanical effects, could outperform classical devices in some tasks or scenarios. Despite their potential, verifying that these devices work correctly and truly realize desired quantum states can be challenging, particularly when they cannot be fully examined or inspected.

One approach to verify quantum states or measurements is known as self-testing. This is a technique that allows quantum scientists to confirm the properties of a quantum system solely by analyzing its outputs, instead of examining how it operates internally.

Researchers at Université libre de Bruxelles (ULB), the University of Gdansk, and the Polish Academy of Sciences recently introduced a new universal scheme that could be used to self-test any quantum state or measurement. Their protocol, introduced in a paper published in Nature Physics, works by placing a device within a simple star-shaped quantum network and assessing the correlations between measurements obtained from different outputs that share entangled quantum states, to determine whether they are aligned with theoretical predictions.