Hyper-encoded photon qudits and hyperentanglement can effectively increase the channel capacity and have been widely used in quantum communication field. Photon transmission loss is one of the main obstacles of quantum communication, which can reduce the communication efficiency and even threaten the security. In the paper, we propose a feasible noiseless linear amplification (NLA) protocol for protecting the single-photon qudit and two-photon hyperentanglement encoded in polarization and double-longitudinal momentum degrees of freedom (DOFs). The NLA protocol is in linear optics, and especially, it adopts practical imperfect single photon sources to generate auxiliary photons. As a result, it can be realized under current experimental condition. By performing the NLA protocol, we can increase the fidelity of target qudit and hyperentanglement and preserve their encoding features in all DOFs. This NLA protocol has application potential in current and future high-capacity quantum communication field.

超编码光子量子态和超纠缠可以有效地增加信道容量，已被广泛应用于量子通信领域。光子的传输损耗是量子通信的主要障碍之一，它会降低通信效率，甚至威胁到安全性。在本文中，我们提出了一种可行的无噪声线性放大（NLA）协议，用于保护以极化和双纵向动量自由度（DOFs）编码的单光子qudit和双光子超纠缠。NLA协议是线性光学中的协议，尤其是它采用了不完美的实际单光子源来生成辅助光子。结果，可以在当前的实验条件下实现。通过执行NLA协议，我们可以提高目标数量和超纠缠度的保真度，并在所有自由度中保留其编码特征。该NLA协议在当前和未来的大容量量子通信领域具有应用潜力。