Experimental setup for the realization and the processing of the four-partite three-level two-photon cluster state

Prof. Morandotti’s group demonstrates a universal entanglement witness operators capable of detecting any pure quantum state with feasible measurement.

Entanglement is an essential resource in quantum information science and its presence in any quantum system can be experimentally detected through entanglement witness operators. In recent years, the experimental generation of complex quantum states has intensified the need for witnesses that are capable of detecting such systems and are experimentally optimal at the same time. This means that the witness should require a measurement setting that is reduced in number and complexity, as well as include only single-qudit projections, while still possessing a high noise tolerance. However, ‘experimentally-friendly’ witnesses capable of accomplishing these tasks have not been derived yet.

Here, we provide a universal method to construct experimentally-optimal witnesses capable of detecting the presence as well as the entanglement of any arbitrarily-complex pure quantum state. Furthermore, the derived approach allows to customize these witness operators towards experimental restrictions and/or accessible measurement settings. We explicitly derive a witness capable of detecting genuine multipartite entanglement of d-level cluster states and demonstrate that these are more noise tolerant than their two-level counterparts, as well as that the noise robustness increases as the number of levels increases.

Link for access to the article: Universal N-Partite d-Level Pure-State Entanglement Witness Based on Realistic Measurement Settings