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Experimental realization of narrowband four-photon GHZ state in single cold atomic ensemble

The group of Bao-Sen Shi attain remarkable progress in direction of cold atom. We realized that the generation of narrowband four-photon GHZ state in single cold atomic ensemble.

Multi-photon entangled states not only play a crucial role in researching on quantum physics but also have many applications in quantum information field such as quantum computation, quantum communication and quantum metrology. To fully exploit the multi-photon entangled states, it is important to establish the interaction between entangled photons and matter, which requires photons having narrow bandwidth. Here we report on the experimental generation of narrowband four-photon Greenberger-Horne-Zeilinger state with a fidelity of 64.9% through multiplexing two spontaneously four-wave mixings in a cold 85Rb atomic ensemble. The full-bandwidth of generated GHZ state is about 19.5 MHz. Thus, the generated photons can match the atoms effectively, which are very suitable for building up quantum computation and quantum communication network based on atomic ensembles.

Fig. 2. (a) The measured four-fold coincidence in the H/V basis of GHZ

state. (b)The measured four-fold coincidence in the HHHH basis.