Quantum communication can realize secure information transmission based on the fundamental principles of quantum mechanics. Photon is a crucial information carrier in quantum communication. The photonic quantum communication protocols require the transmission of photons or photonic entanglement between communicating parties. However, during this process, photon transmission loss inevitably occurs due to environmental noise. Photon transmission loss significantly reduces the efficiency of quantum communication and even threatens its security, so that it becomes a major obstacle for practical long-distance quantum communication. Quantum noiseless linear amplification (NLA) is a promising method for mitigating photon transmission loss. Through local operations and post-selection, NLA can effectively increase the fidelity of the target state or the average photon number in the output state while perfectly preserve the encoded information of the target state. As a result, employing NLA technology can effectively overcome photon transmission loss and extend the secure communication distance.
In this paper, we categorize existing NLA protocols into two classes: the NLA protocols in DV quantum systems and CV quantum systems. In DV quantum systems, we provide a detailed introduction of the quantum scissor (QS)-based NLA protocols for single photons, single-photon polarization qubits, and single-photon spatial entanglement. The QS-based NLA can effectively increase the fidelity of the target states while perfectly preserve its encodings. In recent years, researchers have researched on various improvement on QS-based NLA protocols. In CV quantum systems, researchers adopted parallel multiple QSs structure, generalized QS to increase the average photon number of the Fock state, coherent states and two-mode squeezed vacuum state. Beyond theoretical progress, experimental implementations of NLA have also made significant progresses. We summarize representative experimental demonstrations of QS-based NLA protocols.
In the concluding section, we provide perspectives on future development directions for NLA to facilitate its practical applications. This review can provide theoretical support for the practical development of NLA in the future.