Long-distance quantum communication holds significant promises for information transmission over extremely large distances. However, ensuring communication security over extensive distances poses considerable challenges. In this article, we propose a new approach to long-distance quantum communication that is carried out in an information-carrying particle-free manner, known as counterfactual quantum communication. Our approach extends the counterfactual transmission signal by leveraging quantum repeaters situated between distant nodes, facilitating counterfactual entanglement swapping. Due to the absence of information-carrying particles in the channel, it enhances the security of information transmission. We demonstrate that our proposed protocol not only establishes the direct communication link between distant nodes, but also generates redundant communication links between neighboring nodes, enhancing resilience against primary link failures. Furthermore, we provide numerical simulations of C-Swap gate and counterfactual long-distance quantum communication scenarios to quantify success probabilities where the photon is not lost during the counterfactual communication.
Long-distance quantum communication holds significant promises for information transmission over extremely large distances. However, ensuring communication security over extensive distances poses considerable challenges. In this article, we propose a new approach to long-distance quantum communication that is carried out in an information-carrying particle-free manner, known as counterfactual quantum communication. Our approach extends the counterfactual transmission signal by leveraging quantum repeaters situated between distant nodes, facilitating counterfactual entanglement swapping. Due to the absence of information-carrying particles in the channel, it enhances the security of information transmission. We demonstrate that our proposed protocol not only establishes the direct communication link between distant nodes, but also generates redundant communication links between neighboring nodes, enhancing resilience against primary link failures. Furthermore, we provide numerical simulations of C-Swap gate and counterfactual long-distance quantum communication scenarios to quantify success probabilities where the photon is not lost during the counterfactual communication.
Counterfactual quantum communication enables communication between remote parties without transmitting any information-carrying particle. In this paper, we propose four protocols for secure quantum communication networks utilizing such communication. The first protocol, counterfactual quantum secure direct communication (CQSDC), enables a sender to securely and counterfactually communicate a secret message. The second protocol, counterfactual quantum secure dialogue (CQSD), allows legitimate parties to transmit secret messages in each direction simultaneously, securely and counterfactually. The third protocol, counterfactual controlled quantum teleportation (CCQT), facilitates a sender to counterfactually teleport a quantum state to a receiver under the supervision of a controller. Finally, the fourth protocol, counterfactual quantum private comparison (CQPC), capacitates a third party to compare the private states of the end parties without the actual knowledge of the counterfactually transmitted states. We devise the CQSDC and CQSD protocols by exploiting the counterfactual Swap, dual chained quantum Zeno (CQZ), and distributed controlled NOT gates. For CCQT and CQPC protocols, we utilize CQZ gates with a horizontally polarized photon input. We show that the security of CQSDC and CQSD relies on counterfactual entanglement swapping, while that of CCQT and CQPC depends on establishing secure counterfactual communication channels and security validation with decoy particles, respectively.
We propose an alternative entanglement swapping scheme based on the principle of the counterfactual quantum communication, which demonstrates nonlocal entanglement swapping can be achieved by the operations of a third party. During the whole process, it is not needed to transmit any physical particles among the participants. Furthermore, all the entangled particles are not destroyed in the counterfactual entanglement swapping process, which means we can obtain two pairs of nonlocal entanglement at the same time, thus achieve high-efficiency entanglement distribution. The numerical analysis about the performance of the presented scheme shows that this counterfactual protocol can be implemented with high success probability and fidelity in the ideal asymptotic limit. The scheme may be meaningful for large-scale quantum communication network and quantum repeater.
Quantum communication holds the promise of achieving long-distance secure message transmission by exploiting quantum entanglement between remote locations. Quantum repeaters are indispensable to the realization of quantum networks for long-distance quantum communication. Similar to its classical analogue, a good quantum repeater should be able to compensate channel attenuation with a quantum amplifier, and to combat channel distortion through a quantum equaliser. This quantum repeater should also operate by an efficient and robust protocol. The first part of this project researches the continuous mode operation of a noiseless linear amplifier (NLA). We develop a dynamical model to describe the operation of the nondeterministic NLA in the regime of continuous-mode inputs. Both the quantum scissor based NLA and the photon addition-subtraction based NLA are analysed. Simulation results are also presented to confirm theoretical analysis. The second part proposes two quantum protocols. An atomic ensemble based quantum protocol is developed to generate distributed W-states. These generated distributed W-states could be considered as an entanglement resource between more than two distant nodes and would be useful in quantum communication and distributed quantum computation in the future. We also propose a protocol by which quantum key distribution can be achieved deterministically between multiple nodes.This deterministic quantum key distribution scheme may be used to guarantee secure communication for wireless sensor networks and Internet of Things. The last project analyses distortion of quantum channels and develops physically realisable modules to combat it. The minimum phase channel and non-minimum phase all pass channel are discussed separately.
Long-distance transfer of quantum information is an essential ability for many applications of quantum science. A natural choice to distribute quantum information is to encode it into photons and transfer it through optical fibers. However, due to the unavoidable transmission losses present in every communication channel, the distances for efficient quantum communication via direct-state transfer are limited to a few hundred kilometers. To overcome this limitation, the use of quantum repeaters has been suggested. A quantum repeater protocol aims to establish entanglement (i.e., quantum correlation) between remote nodes by first generating entanglement over shorter distance pieces, storing it in quantum memories, and finally extending it to the whole distance using entanglement swapping. The main goal of this thesis is to design quantum repeater architectures using single solid-state quantum emitters and to develop the two-qubit gates required for performing entanglement swapping. We first explain the basic ideas of quantum repeaters and introduce potential material candidates, single erbium (168Er) and europium (151Eu) ions doped yttrium orthosilicate photonic crystals. Next, we propose a quantum repeater scheme combing erbium and europium ions to generate and distribute entanglement over long distances. We study the entanglement generation rate of the protocol and compare it with the rate of a well-known ensemble-based quantum repeater. Then, using cavity assisted interactions, we propose three different schemes to perform high fidelity two-qubit gates between single quantum systems. We quantify their expected performance in detail by taking into account many realistic imperfections and compare their strengths and weaknesses. The ability to perform local two-qubits gates is especially crucial in terms of distributing entanglement. Finally, based on our gained knowledge through these projects, we propose our second quantum repeater architecture based on erbium (167Er) ions, which outperforms the first scheme. We study two possibilities for distributing entanglement and calculate the overall fidelity as well as the distribution rate of the protocol.
Quantum entanglement, a bizarre and fundamental phenomenon in quantum mechanics, offers a tantalizing pathway to information transfer beyond the limitations of classical physics. This research investigates the feasibility of utilizing quantum entanglement for ultra-long-distance information transmission, proposing a novel protocol leveraging entangled states to achieve this goal. The core mechanism centers around establishing quantum entanglement networks and employing sophisticated protection mechanisms to mitigate potential risks associated with information leakage. The proposed protocol aims to overcome the current barriers to quantum communication, offering a potentially transformative approach to secure and long-distance data exchange. This paper explores the theoretical underpinnings, design considerations, and potential challenges associated with implementing this advanced communication paradigm. The core claim is that this protocol can facilitate the transmission of information across unprecedented distances, potentially revolutionizing secure communication and fundamental scientific research.
Long-distance quantum communication faces significant challenges due to photon loss and operational errors in fiber optic channels. Quantum repeaters (QRs) offer a promising solution by extending the communication range and enabling secure exchange of quantum information over continental distances. This article provides an overview of the three generations of QRs, comparing their technological requirements and challenges. We introduce the basic techniques, such as entanglement swapping, distillation, and error correction, and discuss their relevance to each generation of QRs. In addition, we present a future direction that integrates superconducting qubits with optical fibers, enabled by recent advances in microwave-optical transduction. This new hybrid architecture offers promising prospects for scalable and efficient quantum networks. It is also applicable in quantum key distribution protocols, such as E91.