We present several experimental progresses for advanced quantum communication based on multi-photon entanglement. Quantum secret sharing (QSS) and third-man quantum cryptograph (TQC) shows the advancement in multi-party quantum communication. Quantum error rejection (QER) holds the promise for error-free transfer in long-distance quantum communication. Fault-tolerant quantum cryptography in a decoherence-free subspace (DFS) and quantum-relay-assisted key distribution respectively overcome the difficulties caused by decoherence and photon loss, the two main crucial problems in long-distance quantum communication.
We present several experimental progresses for advanced quantum communication based on multi-photon entanglement. Quantum secret sharing (QSS) and third-man quantum cryptograph (TQC) shows the advancement in multi-party quantum communication. Quantum error rejection (QER) holds the promise for error-free transfer in long-distance quantum communication. Fault-tolerant quantum cryptography in a decoherence-free subspace (DFS) and quantum-relay-assisted key distribution respectively overcome the difficulties caused by decoherence and photon loss, the two main crucial problems in long-distance quantum communication.
Quantum secret sharing (QSS) and third-man quantum cryptography (TQC) are essential for advanced quantum communication; however, the low intensity and fragility of the multiphoton entanglement source in previous experiments have made their realization an extreme experimental challenge. Here, we develop and exploit an ultrastable high intensity source of four-photon entanglement to report an experimental realization of QSS and TQC. The technology developed in our experiment will be important for future multiparty quantum communication.
This paper presents an investigation of practical quantum secure communication using multi-photon tolerant protocols. Multi-photon tolerant protocols loosen the limit on the number of photons imposed by currently used quantum key distribution protocols. The multi-photon tolerant protocols investigated in this paper are multi-stage protocols that do not require any prior agreement between a sender Alice and a receiver Bob. The security of such protocols stems from the fact that the optimal detection strategies between the legitimate users and the eavesdropper are asymmetrical, allowing Bob to obtain measurement results deterministically while imposing unavoidable quantum noise to the eavesdropper Eve's measurement. Multi-photon tolerant protocols are based on the use of transformations known only to the communicating party applying them i.e. either Alice or Bob. In this paper multi-photon tolerant protocols are used in order to share a key or a message between a sender Alice and a receiver Bob. Thus such protocols can be either used as quantum key distribution (QKD) protocols or quantum communication protocols. In addition, multi-stage protocols can be used to share a key between Alice and Bob, followed by the shared key used as a seed key to a single-stage protocol, called the braiding concept. This paper presents a practical study of multi-photon tolerant multi-stage protocols. Security aspects as well as challenges to the practical implementation are discussed. In addition, secret raw key generation rates are calculated with respect to both losses and distances over a fiber optical channel. It is well-known that raw key generation rates decreases with the increase in channel losses and distances. In this paper, coherent non-decoying quantum states are used to transfer the encoded bits from Alice to Bob. Raw key generation rates are calculated for different average photon numbers µ and compared with the case of µ=0.1, which is the average number of photons used in most single-photon based QKD protocols. Furthermore, an optimal average number of photons to be used within the secure region of the multi-photon tolerant protocols is calculated. It is worth noting that, with the increased key generation rates and distances of communication offered by the multi-photon tolerant protocols, quantum secure communication need not be restricted to quantum key distribution; it can be elevated to attain direct quantum secure communication.
After the preceding four introductory chapters, we are finally ready to discuss optical quantum information processing. While in principle quantum communication can be implemented with atoms or electrons, in practice the implementation of choice for long-distance quantum communication will almost certainly be optical. In this chapter, we will develop some of the key topics in quantum communication with single photons, and we will discuss continuous-variable quantum communication in Chapter 8. In some ways, quantum communication is the most technologically advanced part of quantum information processing. Most protocols in this chapter, such as teleportation and cryptography, have been convincingly demonstrated in the lab, and there are already several commercial organizations that sell cryptographic systems based on quantum mechanical principles. In particular, the promise of secure communication with quantum cryptography is one of the driving forces behind the development of single-photon sources and detectors. In this chapter, we first construct several optical representations of the qubit, including polarized photons and time-bin encoding. Since the single-photon implementation of a qubit is central to optical quantum information processing, this constitutes a large part of the chapter. In Section 5.2 we discuss quantum teleportation and entanglement swapping with single photons. We also present a method for entanglement distillation using entanglement swapping. In Section 5.3 we introduce decoherence-free subspaces, which can be used to reduce noise in the transmission of quantum information, and even establish communication channels in the absence of shared reference frames.
Entanglement distribution is a fundamental building block of quantum communication networks, enabling the secure and reliable exchange of quantum information over long distances. Unlike classical communication, quantum networks exploit the unique properties of quantum entanglement to support applications such as quantum key distribution, quantum teleportation, distributed quantum computing, and networked quantum sensing. Although significant progress has been made in recent years, the efficient generation, transmission, and preservation of entangled states remain major research challenges due to photon loss, decoherence, and limitations in current communication infrastructure.This review provides a comprehensive overview of entanglement distribution in quantum communication networks, focusing on the technologies that enable practical implementation and the latest experimental developments. It discusses key approaches for generating and distributing entangled photons through optical fibers, free-space links, and satellite-based communication, together with supporting technologies such as quantum repeaters, quantum memories, and photonic devices. The review also examines recent experimental demonstrations that have advanced long-distance quantum communication while highlighting the technical barriers that must be overcome for large-scale deployment. Finally, emerging applications and future research directions are presented, including the development of scalable quantum networks, the quantum internet, and secure global communication systems. This review aims to provide researchers and students with a clear understanding of the current state of entanglement distribution and its growing role in next-generation quantum communication technologies.
A quantum internet is one of the promises of the second quantum revolution. New difficulties arise when the first quantum network (QN) hardware prototypes get closer to completion. The development of scalable QN systems is still in its early stages, yet a functioning network is more than simply the physical tools. The proposed method offers a QN protocol that addresses the novel conceptual and technological difficulties posed by quantum physics and enables end-to-end quantum communication. As the key procedure in quantum information science, quantum entanglement swapping (QES) has the potential to revolutionise QN communication. The suggested paradigm, which considers entanglement, enables safe communication utilising a trusted third party across a long-distance QN. The protocols might act as the basic structure of a future quantum internet. Even if scaling and entanglement coherence issues must be overcome, this research provides the groundwork for improving error-correcting codes and fault-tolerant quantum computers.