Quantum complementarity: A novel resource for unambiguous exclusion and encryption

Understand

Complementarity is a phenomenon explaining several core features of quantum theory, such as the well-known uncertainty principle.

• Roughly speaking, two objects are said to be complementary if being certain about one of them necessarily forbids useful knowledge about the other.
• Two quantum measurements that do not commute form an example of complementary measurements, and this phenomenon can also be defined for ensembles of states.
• Although a key quantum feature, it is unclear whether complementarity can be understood more operationally, as a necessary resource in some quantum information task.