Heralded Noiseless Linear Amplification For Single-Photon Encoded In Three Degrees Of Freedom

In quantum communication research,photons have become the main information carriers due to their operability and high-speed transmission properties.Optical qubits and photon entanglement are important resources in the field of quantum communication,and are widely used in quantum teleportation,quantum key distribution,quantum secure direct communication and other fields.In long-distance quantum communication,photon transmission loss is an important obstacle to quantum communication.Photon transmission loss causes the propagation of photons in optical fibers to exhibit exponential decay with the increase of channel length.Photon transmission loss not only seriously affects the communication efficiency of quantum communication,limits the communication length,but also threatens the security of quantum communication.To address the above problems,quantum noise-free linear amplification(NLA)was proposed,which is widely used to protect singlephoton qubits and quantum entanglement.The first work in this paper utilizes imperfect single-photon source assistance to achieve noiseless linear amplification forsingle-photon qudit andt wo-photon hyperentanglement encodedin three degrees of freedom.The photon qudits which are simultaneously encoded in several degrees of freedom can effectively increase the channel capacity,so as to improve the communication efficiency of quantum communication.Experimentally,three degrees of freedom,such as polarization and dual longitudinal momentum of a single photon,have been realized at the same time.The scheme of this paper can improve the fidelity of target quantum state and preserve their encoded features in all degrees of freedom.This scheme can be further extended to two-photon superentangled state systems.The NLA protocol is in linear optics,which can be applied under the current experimental conditions and have stronger practicability.The second work in this paper proposes a device-independent quantum-secure direct communication(DI-QSDC)scheme based on a single-photon source.DIQSDC allows senders to send secret messages directly to receivers without first sharing a key and is resistant to all attacks from imperfect devices.In this paper,we introduce novel photonic protocols for DI-QSDC exploiting single-photon sources and heralding-type architectures.The secrete message capacity and the maximum communication distance of this scheme are obviously better than the previous DI-QSDC scheme.It is expected to play a role in the construction of quantum networks in the future.