Hyperentanglement is a quantum system which simultaneously entangles in several degrees of freedom. It is an important resource in quantum communication field. In practical application of hyperentanglement, the photon transmission loss is a big obstacle. In the paper, we propose an entanglement-assisted noiseless linear amplification (NLA) protocol to protect the two-photon polarization–time-bin hyperentanglement. Our protocol can effectively increase the fidelity of this hyperentanglement, while preserve its polarization and time-bin features. Our NLA protocol can be realized under current experimental condition and further extended to protect the general N-photon polarization–time-bin hyperentanglement in the multi-directional transmission process. This NLA protocol may have important applications in future hyperentanglement-based quantum communication network field.

中文翻译：

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纠缠辅助的无噪声线性放大，用于任意两个光子极化-时空超纠缠

超纠缠是一个同时纠缠几个自由度的量子系统。它是量子通信领域的重要资源。在超纠缠的实际应用中，光子的传输损耗是一个很大的障碍。在本文中，我们提出了一种纠缠辅助的无噪声线性放大（NLA）协议，以保护双光子极化-时区超纠缠。我们的协议可以有效地增加这种超纠缠的保真度，同时保留其极化和时限特征。我们的NLA协议可以在当前的实验条件下实现，并可以进一步扩展以保护通用N多方向传输过程中的光子极化-时空超纠缠。该NLA协议在未来基于超纠缠的量子通信网络领域中可能具有重要的应用。