Quantum repeaters enable long-range quantum communication in the presence of attenuation. Here we propose a method to construct a robust quantum repeater network using only existing technology. We combine the ideas of brokered graph-state construction with double-heralded entanglement generation to form a system that is able to perform all parts of the procedure in a way that is highly tolerant to photon loss and imperfections in detectors. We show that when used in quantum key distribution this leads to secure kilohertz bit rates over intercontinental distances.
Quantum repeaters enable long-range quantum communication in the presence of attenuation. Here we propose a method to construct a robust quantum repeater network using only existing technology. We combine the ideas of brokered graph-state construction with double-heralded entanglement generation to form a system that is able to perform all parts of the procedure in a way that is highly tolerant to photon loss and imperfections in detectors. We show that when used in quantum key distribution this leads to secure kilohertz bit rates over intercontinental distances.
The problem of distributing a secret key by quantum channels is one of the preeminent problems in quantum information. To construct such a quantum channel, it is useful to use quantum repeaters, which shorten the distance over which individual photons need to be sent, and thus overcoming the problem of attenuation. Here, we present a method by which a quantum repeater network may be constructed using only existing technology. By taking advantage of the robustness of the processes of double-heralding and brokering, a thorough analysis of the system shows that this gives secret key rates on the order of kilohertz, even over distances of thousands of kilometres.
Abstract: This chapter explores the engineering of quantum repeaters, a critical technology for enabling secure and scalable long-distance quantum communication. Quantum repeaters extend the range of quantum communication networks by preserving entanglement and mitigating signal loss over large distances. The chapter covers the key principles of entanglement swapping, quantum memory, and quantum error correction, which are essential for maintaining the integrity of quantum states. It also examines advanced repeater architectures, including multi-mode repeaters and entanglement purification techniques, to improve scalability and robustness. Case studies highlight real-world implementations of quantum repeaters in quantum key distribution (QKD) networks, demonstrating their role in achieving secure global communication. Keywords: quantum repeaters, long-distance quantum communication, entanglement swapping, quantum memory, quantum error correction, entanglement purification, multi-mode repeaters, quantum key distribution, QKD, scalable quantum networks, secure communication.
Quantum networking, heralded as the next frontier in communication networks, envisions a realm where quantum computers and devices collaborate to unlock capabilities beyond what is possible with the Internet. A critical component for realizing a long-distance quantum network, and ultimately, the Quantum Internet, is the quantum repeater. As with the race to build a scalable quantum computer with different technologies, various schemes exist for building quantum repeaters. This article offers a gentle introduction to the two-way “all-photonic quantum repeaters,” a recent addition to quantum repeater technologies. In contrast to conventional approaches, these repeaters eliminate the need for quantum memories, offering the dual benefits of higher repetition rates and intrinsic tolerance to both quantum operational errors and photon losses. Using visualization and simple rules for manipulating graph states, we describe how all-photonic quantum repeaters work. We discuss the problem of the increased volume of classical communication required by this scheme, which places a huge processing requirement on the end nodes. We address this problem by presenting a solution that decreases the amount of classical communication by three orders of magnitude. We conclude by highlighting other key open challenges in translating the theoretical all-photonic framework into real-world implementation, providing insights into the practical considerations and future research directions of all-photonic quantum repeater technology.
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 quantum communication requires quantum repeaters to overcome photon loss in optical fibers. Here we demonstrate a repeater node with two memory atoms in an optical cavity. Both atoms are individually and repeatedly entangled with photons that are distributed until each communication partner has independently received one of them. An atomic Bell-state measurement followed by classical communication serves to establish a key. We demonstrate scaling advantage of the key rate, increase the effective attenuation length by a factor of 2, and beat the error-rate threshold of 11% for unconditionally secure communication, the corner stones for repeater-based quantum networks.
Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥ 1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.