Verifying Entanglement with Limited Data
Quantum communication, quantum computing, and quantum sensing all depend on quantum entanglement—particle correlations that have no classical counterpart. Consequently, scientists have been pursuing methods for verifying the presence of entanglement in a practical and reliable way. Now Joonwoo Bae at the Korea Advanced Institute of Science and Technology and his colleagues have demonstrated such a validation method [1]. The technique can be readily applied to a wide range of realistic scenarios, especially ones where only a limited set of measurements on the quantum system is possible.
The new approach works by taking available measurement data—which would be insufficient to reconstruct the system’s full quantum state—and turning them into a family of so-called entanglement witnesses. These are specially chosen observables that can certify entanglement when their average values fall outside certain bounds. In the researchers’ method, some witnesses are obtained by systematically transforming simple initial candidates through an operation known as mirroring. Others are found via a numerical optimization procedure that searches for those witnesses best suited to reveal entanglement under the given measurement constraints.
Bae and his colleagues demonstrated their technique experimentally by generating pairs of polarization-entangled photons and measuring them in just a few polarization settings. The researchers then used the resulting, limited data to construct witnesses that confirmed the photons’ entanglement. This work provides the first demonstration of mirrored witnesses in the lab. It also makes witnesses more practical by showing how they can be used to efficiently verify entanglement and establishes a link with existing theoretical methods for detecting entangled states.
–Ryan Wilkinson
Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.
References
- J. Seong et al., “Practical and efficient verification of entanglement with incomplete measurement settings,” APS Open Sci. 1, 000008 (2026).