Generation of a bright four-photon entangled state from a warm atomic ensemble via inherent polarization entanglement

• Published in: Applied physics letters 2022-01, Vol.120 (2)
• Main Authors: Park, Jiho, Moon, Han Seb
• Format: Article
• Language: English
• Subjects: Angular momentum; Applied physics; Atomic states; Entangled states; Entanglement; Four-wave mixing; Multiplexing; Photons; Polarization; Signal processing
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0076851

We report the stable generation of a bright four-photon polarization-entangled Greenberger–Horne–Zeilinger (GHZ) state obtained by the spatial multiplexing of inherently polarization-entangled photons from a warm atomic ensemble of 87Rb. Owing to the total angular momentum conservation of the atomic state in the spontaneous four-wave mixing process of a cascade-type atomic system, the polarizations of the signal and idler photons in the two-photon decay are entangled. With a Rb vapor cell, we realize the generation of robust and bright four-photon GHZ states using two symmetrical spatial modes of inherently polarization-entangled photon pairs without applying an interferometric configuration. The four-photon average coincidence rate of the GHZ state with a fidelity of 0.88(2) is measured as 1.69(7) Hz under a weak pump power of 10 μW. The minimum Allan variance for the stability of the four-photon GHZ state is estimated as 0.92° for an average time of 10 h.