Experimental few-copy multipartite entanglement detection

The reliable verification of quantum entanglement is an essential task to scale up quantum technologies. Although progressively more efficient techniques have been developed, most of these focus solely on minimizing the number of measurement settings. Recently, a single-shot probabilistic method was proposed [1], wherein it was shown that even a single detection event can be sufficient to verify if a state exhibits entanglement. In our work [2] we extend this theoretical approach by showing that any entanglement witness can be translated into this probabilistic framework. To prove our findings, we report the experimental entanglement verification in a photonic six-qubit cluster state. We find that the presence of entanglement can be certified with at least 99.74% by using only 20 copies of the state, and that genuine six-qubit entanglement is verified with at least 99% confidence by using 112 copies of state. This novel method entails a significant reduction of resources, promising a great impact in future experiments where an efficient and resource saving approach will be essential for entanglement verification problems in multi-qubit states.
[1] A. Dimić et al., npj Quantum Information, 4(1), 11 (2018).
[2] V. Saggio et al., Nat. Phys. 15, 935–940 (2019).