Multi-photon entangled states play a crucial role in quantum information applications such as secure quantum communication, scalable computation, and high-precision quantum metrology. Quantum memory for entangled states is a key component of quantum repeaters, which are indispensable in realizing quantum communications. Storing a single photon or an entangled photon has been realized through different protocols. However, there has been no report demonstrating whether a multi-photon state can be stored in any physical system or not. Here, we report on the experimental storage of a two-photon NOON state in a cold atomic ensemble. Quantum interference measured before and after storage clearly shows that the properties of the two-photon NOON state are preserved during storage. Our experiment completes the first step towards storing a multi-photon entangled state.
@article{arxiv.1701.03317,
title = {Interfacing a two-photon NOON state with an atomic quantum memory},
author = {Wei Zhang and Ming-Xin Dong and Dong-Sheng Ding and Shuai Shi and Kai-Wang and Zhi-Yuan Zhou and Guang-Can Guo and Bao-Sen Shi},
journal= {arXiv preprint arXiv:1701.03317},
year = {2018}
}