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Conference on Lasers and Electro-Optics

Multipartite d-level photon cluster states and practical entanglement detection through witness operators

Stefania Sciara, Christian Reimer, Piotr Roztocki, David Moss, Lucia Caspani, William J. Munro, Michael Kues, Roberto Morandotti

Published Jan 1, 2021• 0 citations
Publisher

Abstract

We develop witness operators enabling the practical detection of arbitrary complex photon states and apply them to validate the entanglement of the first multipartite d-level cluster state achieved through simultaneous time- and frequency-entanglement.
DOI
10.1364/cleo_qels.2021.fm1n.3

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Certifying entanglement of a multipartite state is generally considered a demanding task. Since an N qubit state is parametrized by 4^{N}-1 real numbers, one might naively expect that the measurement effort of generic entanglement detection also scales exponentially with N. Here, we introduce a general scheme to construct efficient witnesses requiring a constant number of measurements independent of the number of qubits for states like, e.g., Greenberger-Horne-Zeilinger states, cluster states, and Dicke states. For four qubits, we apply this novel method to experimental realizations of the aforementioned states and prove genuine four-partite entanglement with two measurement settings only.