The past decade has brought significant progress in Quantum Information Science (QIS), the field focused on developing quantum systems for advanced information processing, sensing, and communication that surpass classical capabilities. While quantum computing has been the centerpiece of public attention, quantum networking and the quantum internet are rapidly gaining traction across scientific, industrial, and security sectors, thanks to their potential for enabling ultra-secure communication.
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QIS has evolved from a theoretical idea that was initially put forth by pioneers such as Richard Feynman in 1981. With traditional computing reaching inherent physical and economic limits to increasing power, evidenced by the slowdown in expected computational growth, research institutions and industry worldwide have shifted their focus toward quantum technologies1. An intriguing topic within this quantum revolution is the quantum internet, built from landmark developments like the BB84 protocol for quantum key distribution (QKD), the development of quantum teleportation, and the first commercial QKD systems2.
Entanglement, which is a fundamental property of quantum systems, is essential for developing any quantum technology. Thanks to their unique physical properties, such as being charge-neutral and massless, photons offer a highly promising platform for long-distance entanglement, a key requirement for building quantum internet infrastructure.3 Photonic entanglement can also be generated at room temperature, making it attractive for scaling.
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What Is Entanglement?
One special characteristic found only in quantum systems is entanglement. When a coin is tossed, there are two possible outcomes; head or tail. Assume that two users, Alice and Bob, independently toss their coins in two different places. The outcome of every coin flip will be entirely random; there will be no correlation between the two. According to quantum mechanics, the two coins can get entangled if they are regarded as quantum states. Alice and Bob toss the entangled coins independently in two different places, and the results are the same. Bob will also have a "head" when Alice does, no matter how far away they are. Albert Einstein called this phenomenon "spooky action at a distance" and it is known as quantum entanglement.
Photons are ideal carriers of entangled states because they travel at the speed of light, allowing for fast communication, and interact only weakly with their environment. This weak interaction helps minimize decoherence, making it possible to preserve entanglement over long distances.
Quantum Internet
Building and scaling quantum-protected communication networks is widely regarded as one of the 21st century's most important technological frontiers. The research community believes that a quantum internet is closer to being used in practice, ahead of a general-purpose quantum computer. Significant advancements have been made possible by global investment in QIS, such as the Micius satellite successfully demonstrating QKD over intercontinental distances4, enabling "hack-proof" communication and the first long-distance quantum data transfer over 410km of standard optical fiber in the UK in 2025.6 These tests confirm the fundamental concepts required to build a complete quantum network.
The Quantum Network Stack
To build a functional prototype of the quantum internet, a layered architecture, known as the quantum network stack, must be developed. This framework is similar in concept to the one used in classical networking, providing structure and organization to the design and operation of quantum networks.1,3 The physical layer, which includes all quantum hardware components and the optical cables that carry quantum data, is the fundamental layer. Among its duties are the creation, timing, and synchronization of quantum information. The data connection layer sits above this, overseeing the physical layer creating photonic entanglement.
The task of creating long-distance entanglement between nodes that are not directly coupled falls to the network layer. Entanglement switching, which makes use of the link layer to create chains of entanglement across intermediary photonic nodes, accomplishes this vital task. The transport layer then uses teleportation to guarantee the predictable transfer of qubits. Lastly, the application layer allows end-user programs to exploit both the classical and quantum network capabilities for tasks such as secure data transfers or entangling the photonic qubits of distant quantum computers.
Building Blocks of the Quantum Internet
Components must meet stringent reliability, scalability, and maintenance requirements in order to build scalable, wide-area quantum networks. High-speed, low-loss quantum switches, multiplexing technologies, quantum memory with effective optical interfaces, and transducers to translate quantum signals between the optical and telecommunications domains are all necessary components.1,3 Advancing quantum networking also depends on several key technologies, including quantum-limited detectors, low-loss optical components, and reliable sources of entangled photons. Additionally, short-range entanglement distribution systems, along with the development of quantum memory architectures and small-scale quantum processors compatible with photon-based qubits at optical or telecom wavelengths, are essential to move the field forward.
The requirement for an analog of the classical signal strengthening and path selection methods is a significant obstacle for quantum networks, especially when creating relayed networks. An analogous technique for enhancing quantum signals or replicating entanglement over several users is vital and challenging, in contrast to classical networks where signal boosting is simple. Managing the various types of quantum entanglement production, switching, and purification becomes more difficult as a result.
Quantum repeaters are essential for expanding the entanglement distribution range beyond the roughly 100-kilometer limit imposed by fiber attenuation1. By using the resource of a second entangled pair, a quantum repeater "hops" the entanglement property across an extra distance interval, in a process called entanglement swapping, instead of amplifying the quantum state. Photonic entanglement is well-suited for quantum communication networks because photons can travel long distances while maintaining coherence. Functional quantum memories, capable of storing one half of an entangled pair after a successful transmission, are crucial for realizing the full capabilities of quantum repeaters, which are key to extending the range and reliability of quantum networks. This increases the likelihood of success over long distances and permits significantly higher distribution rates by eliminating the necessity for both pairs required for entanglement switching to survive and arrive simultaneously. For example, four heralded quantum memories are needed for a prototype one-hop repeater.
Current Research Engagement and Industry Landscape
Government research hubs, in collaboration with university labs, spinouts, and established companies, are actively working on the development of quantum internet architecture. This collaborative approach brings together diverse expertise and resources to tackle the complex challenges involved in building scalable, secure quantum networks. For example, the European Quantum Internet Alliance or DARPA’s quantum network initiatives are supporting QuTech in the Netherlands and Harvard-MIT CQuIC in the US respectively. Commercial enterprises such as Toshiba Quantum Technology, Aliyun (Alibaba), PsiQuantum, Cisco, Aliro Quantum, and Sparrow Quantum create technologies for quantum networking, security, and internet applications.
Toward a Global Quantum Network
One key distinction with quantum networks is that, unlike shared states in classical networking, entanglement is intrinsic at the physical layer. In order to allow entanglement distribution, deterministic teleportation, and quantum repeater methods that can compensate for both loss and operational error, it is necessary to find ways to guarantee that network devices achieve fidelity levels that are high enough. The availability of error-correcting devices and concatenated quantum repeaters will signify the final evolution of quantum communication networks.1,3
All protocols, including distributed memory structures, required for distributed quantum computing and quantum sensor applications will be fully supported at this advanced stage. This last step necessitates ongoing advancements in high-fidelity operations, high-repetition-rate quantum connections, and quantum repeater techniques capable of achieving the required fault-tolerant operation depth at every node. Furthermore, for specialized applications like improved quantum sensing, the capacity to produce multipartite entanglement would be essential.
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References and Further Reading
- Awschalom, David. From long-distance entanglement to building a nationwide quantum Internet: report of the doe quantum Internet blueprint workshop. No. BNL-216179-2020-FORE. Brookhaven National Lab.(BNL), Upton, NY (United States), 2020.
- Press, G. (18 May 2021) 27 Milestones In The History Of Quantum Computing.
[Online] Forbes.com. Available at: https://www.forbes.com/sites/gilpress/2021/05/18/27-milestones-in-the-history-of-quantum-computing/
- Sivarajah, I. (16 February 2022) How Photonics is Fueling Quantum Technology Applications. [Online] AZoOptics.com. Available at: https://www.azooptics.com/Article.aspx?ArticleID=2149
- Lu, Chao-Yang, Yuan Cao, Cheng-Zhi Peng, and Jian-Wei Pan. "Micius quantum experiments in space." Reviews of Modern Physics 94, no. 3 (2022): 035001.
- Quantum (8 April 2025) UK achieves quantum communications breakthrough with first long-distance secure data transfer.
[Online] Innovation News Network. Available at: https://www.innovationnewsnetwork.com/uk-achieves-quantum-communications-breakthrough/56987/#:~:text=In%20a%20major%20development%20for,teleportation%20on%20a%20global%20scale.%E2%80%9D
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