Insider Brief
- In a recent paper published on arXiv, Cisco researchers have developed a realistic, modular architecture for integrating quantum networking into classical data centers using photonic interconnects and quantum repeaters.
- Simulations show that even with current hardware limitations, the system can support high rates of entanglement generation suitable for early quantum applications.
- The study emphasizes the importance of fast classical control and synchronization, identifying timing delays as a key bottleneck in practical quantum network performance.
Cisco researchers have laid out a hardware-aware blueprint for integrating quantum networks into classical data center environments, presenting a scalable approach that could bring secure quantum communication closer to commercial use, according to a study.
The study, published earlier this year on the pre-print server arXiv by a team at Cisco Research, centers on building a functional quantum network architecture using photonic links and memory-based quantum repeaters, aiming to overcome the distance limitations of today’s quantum communication systems. Rather than assuming idealized quantum links or futuristic technologies, the researchers write that they modeled a realistic system using known components and explored how classical data center infrastructure could be adapted to accommodate fragile quantum systems.
The work signals a shift from abstract quantum networking concepts to practical engineering, pointing to a future where quantum links could operate side-by-side with classical Ethernet in hyperscale facilities. The study also provides a foundational layer for Cisco’s broader quantum networking strategy, which focuses on advancing key hardware, software and control stack components necessary to build a future quantum internet.
The team writes: “By utilizing shared quantum resources and adopting modular topologies, such as switch-centric and server-centric designs, we achieve on-demand, all-to-all connectivity while minimizing reliance on costly quantum hardware. We developed a network-aware quantum orchestrator and entanglement generation protocols to manage distributed quantum computing jobs, connecting physical-layer architectures with quantum applications. Through simulations and benchmarking, we evaluate the circuit execution capabilities of our architectures, demonstrating the opportunities and challenges in scalability, efficiency, and fidelity.”
From Theory to Deployment
It might be better to start with a basic background of the researcher’s strategy. Essentially, what they are building is a quantum data center.
Quantum networks allow entangled quantum bits — or qubits — to be distributed across distant locations, which could then serve as the backbone of powerful applications such as ultra-secure communication, distributed quantum computing and enhanced sensing. However, transmitting qubits over long distances is constrained by signal loss in optical fibers and the no-cloning theorem, which prevents the use of amplifiers to boost the signal mid-transmission.
To overcome this, quantum repeaters are used to divide the transmission into smaller segments, performing entanglement swapping and purification to extend communication length. While some studies propose quantum networks assuming ideal components, the Cisco team focused on building a more grounded architecture, taking into account the limitations and performance of existing hardware such as entangled photon sources, optical switches, quantum memories and single-photon detectors.
Their proposed data center model includes a tree-shaped optical switch fabric with embedded quantum repeaters and interconnects linking separate memory nodes. In simulations, the researchers tested how quantum states — specifically Bell pairs — could be reliably generated, routed, and stored in the system. The goal was to estimate achievable rates and resource usage for delivering entangled qubits between end nodes.
By examining multiple configurations and loss conditions, the team identified trade-offs in system complexity, latency and performance that will shape the design of real-world quantum networks. This includes the number of memory modules required, the effect of limited coherence times, and the impact of control timing on entanglement distribution rates.
Key Ideas: Paving a Faster Path to Practical Quantum Computing
One of the study’s central findings is that, according to the team’s simulations, even with conservative assumptions on quantum memory lifetime and hardware loss, a modest-scale data center quantum network could still generate hundreds of entangled pairs per second. This suggests that near-term quantum interconnects may support early-stage distributed quantum computing or key distribution applications within localized environments such as data centers or metropolitan areas.
The architecture’s modular design allows it to be extended incrementally, supporting a larger number of end users without a linear increase in complexity. The researchers showed that control latency — how quickly a central controller can process entanglement measurements and issue new commands — is a major performance bottleneck. Even small delays in classical control can significantly degrade entanglement generation rates, pointing to the importance of optimizing classical-quantum co-design.
The study also found that optimizing the routing and storage of Bell pairs across the switch network requires careful timing coordination. Because quantum memories degrade over time, any delay in using an entangled state can result in lower fidelity and higher error rates. Therefore, achieving high throughput in quantum data centers will require fast classical decision-making and synchronization.
Building on Classical Infrastructure
Cisco’s researchers explicitly designed the architecture to be compatible with classical networking infrastructure. The simulated switch layout resembles tree-based topologies commonly used in modern data centers, and the control protocols assume realistic processing and switching times.
This compatibility is a strategic decision on the part of the researchers. Rather than reinventing the entire data center to accommodate quantum links, Cisco appears to be targeting a hybrid future where quantum and classical systems work together. This could ease integration and allow operators to gradually add quantum capabilities to existing fiber networks, reducing capital costs and risk. It could allow data center teams to modify and customize operations, as well, as they adapt to new technological advances.
The team also modeled performance over two different fiber loss scenarios — typical telecom fibers and ultra-low loss fibers — to assess trade-offs in deployment. In both cases, they examined entanglement rates achievable with various numbers of quantum memories per node, allowing data center architects to plan based on performance-cost curves.
The study’s quantitative modeling is based on known benchmarks and measurement data from real quantum devices, such as state-of-the-art photon pair sources, superconducting detectors, and quantum memories. This enables more trustworthy projections than previous work that assumed idealized or future hardware.
Limitations and Open Questions
While the study brings quantum networking closer to practical engineering, there are some key areas for needed future work. First, their architecture assumes the availability of high-fidelity quantum memories and reliable entangled photon sources operating at compatible wavelengths, both of which remain in the early stages of development.
Another limitation is the idealized assumption of perfect Bell pair generation and swap fidelity in their modeling. In practice, noise and decoherence will reduce fidelity, potentially requiring more complex error correction schemes to ensure usable entanglement. The study also does not simulate long-haul fiber networks with multiple hops or free-space optical links, limiting its relevance to data center-scale environments.
The scalability of control will likely be a challenge, too. As the number of nodes grows, the burden on the classical controller to manage entanglement attempts, timing, and routing decisions increases exponentially. This could limit the practicality of centralized control architectures and push toward distributed or hierarchical management in future designs.
While the architecture assumes modular upgrades, retrofitting existing data centers with quantum-compatible fiber paths, temperature-stabilized memory housings, and single-photon detectors will be non-trivial. These practical deployment challenges are not addressed in detail.
Future Directions
Despite these constraints, the study provides a strong foundation for Cisco’s next steps in quantum networking. Immediate priorities likely include experimental prototypes of small-scale networks, further refinement of classical control protocols, and hardware-in-the-loop simulations to validate the assumptions used in the study.
Longer-term, Cisco and the broader community will need to integrate fault-tolerant quantum error correction into the network to support large-scale quantum computing applications. This will require not only better quantum memories and repeaters but also end-to-end orchestration layers that blend classical and quantum operations seamlessly.
Another promising area is the development of quantum-aware routing protocols that can adapt in real time to link degradation and memory decoherence. Similar to how classical networks perform load balancing and rerouting, future quantum networks will need dynamic control to maintain performance under noisy conditions.
The study also opens the door for new standards in quantum data center design, potentially influencing how hardware vendors and network architects build systems for hybrid classical-quantum workloads. Cisco’s experience in shaping traditional internet protocols and standards may position it to play a leading role in this domain.
There’s a sense in the paper that this is just the beginning of a hybrid-quantum computing environment.
“Rather than replacing classical computers as general-purpose systems, quantum computers can excel at specialized tasks,” the team writes. “Exploring the impact of our work on designing modular hybrid architectures—comprising multiple QPUs interconnected with classical HPC nodes—presents an exciting avenue for future research.”
Some Implications for the Industry
The findings are likely to influence not just Cisco’s internal R&D roadmap but also how cloud and hyperscale data center operators approach quantum integration. While universal quantum computing may still be years away, distributed quantum communication, secure key distribution, and early quantum networking services may arrive sooner through architectures like this one.
As more enterprises experiment with quantum key distribution and secure data channels, the ability to scale these solutions beyond point-to-point links will become essential. Cisco’s work shows that with smart architecture and realistic component assumptions, quantum networks in practical environments are not just theoretical — they’re also a question of engineering timelines.
Zooming way out for broader contet, this study aligns with global efforts to create a quantum internet, where entangled particles carry information securely and instantly over long distances. By grounding their approach in deployable hardware and known constraints, Cisco’s researchers help move the conversation from speculation to systems design.
The Cisco team included Hassan Shapourian, Eneet Kaur, Troy Sewell, Jiapeng Zhao, Michael Kilzer, Ramana Kompella, and Reza Nejabati.
Researchers use pre-print servers, such as arXiv to gather feedback about their work in fast-moving fields, such as quantum science. However, the studies are not yet officially peer reviewed, a key step in the scientific process.
The research paper is quite technical. If you would like a deeper technical dive, which this summary story cannot provide, please read the study on arXiv here.
Read more about Cisco’s “entanglement chip” and how the company plans on create a quantum era data center here.
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