Experimental extraction of secure correlations from a noisy private state

Phys Rev Lett. 2011 Jan 21;106(3):030501. doi: 10.1103/PhysRevLett.106.030501. Epub 2011 Jan 18.


We report experimental generation of a noisy entangled four-photon state that exhibits a separation between the secure key contents and distillable entanglement, a hallmark feature of the recently established quantum theory of private states. The privacy analysis, based on the full tomographic reconstruction of the prepared state, is utilized in a proof-of-principle key generation. The inferiority of distillation-based strategies to extract the key is exposed by an implementation of an entanglement distillation protocol for the produced state.