Generation of a time–bin Greenberger–Horne–Zeilinger state with an optical switch

• Published in: Quantum science and technology Vol. 8; no. 3; pp. 35003 - 35009
• Main Authors: Lo, Hsin-Pin, Ikuta, Takuya, Azuma, Koji, Honjo, Toshimori, Munro, William J, Takesue, Hiroki
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.07.2023
• Subjects: GHZ state; optical switch; time–bin qubits
• ISSN: 2058-9565; 2058-9565
• DOI: 10.1088/2058-9565/acc7c2

Abstract Multipartite entanglement is a critical resource in quantum information processing that exhibits much richer phenomenon and stronger correlations than in bipartite systems. This advantage is also reflected in its multi-user applications. Although many demonstrations have used photonic polarization qubits, polarization-mode dispersion confines the transmission of photonic polarization qubits through an optical fiber. Consequently, time–bin qubits have a particularly important role to play in quantum communication systems. Here, we generate a three-photon time–bin Greenberger–Horne–Zeilinger (GHZ) state using a 2 × 2 optical switch as a time-dependent beam splitter to entangle time–bin Bell states from a spontaneous parametric down-conversion source and a weak coherent pulse. To characterize the three-photon time–bin GHZ state, we performed measurement estimation, showed a violation of the Mermin inequality, and used quantum state tomography to fully reconstruct a density matrix, which shows a state fidelity exceeding 70%. We expect that our three-photon time–bin GHZ state can be used for long-distance multi-user quantum communication.