Toshiba will develop and evaluate prototype subsystems designed to make quantum networks easier and more economical to expand using the UK’s existing optical fiber infrastructure. The work will investigate more efficient utilization of network resources and management of connectivity as the number of connected users and sites increases. Improved resource utilization could reduce infrastructure requirements and capital expenditures while making quantum networking services more accessible to telecommunications operators and customers.

UK network operators BT and Colt Technology Services will collaborate on validating the technology against practical network deployment and operational requirements.

Quantum networking and telecommunications infrastructure:

A significant longer-term application of quantum networking is connecting quantum processors located in separate data centers so that they can potentially work together on distributed computational tasks. Interconnecting quantum processors could expand the computational resources available to researchers and organizations and contribute to advances in areas such as pharmaceutical discovery and materials science.   However, scaling quantum networks presents substantial engineering challenges. Unlike conventional optical communications, which transmit classical information using light, quantum networks must distribute and preserve fragile quantum states. This introduces requirements for specialized optical components, quantum-state management, synchronization and, ultimately, quantum repeaters capable of extending quantum communications over longer distances.

Integration with existing carrier fiber infrastructure is another important consideration. Network operators must address fiber loss, optical signal coexistence, routing, resource allocation and operational management while accommodating the specialized requirements of quantum communications.

One potential approach is to multiplex quantum and conventional data channels over the same optical fiber using wavelength-division multiplexing (WDM). This could avoid the expense of deploying entirely separate fiber networks. However, conventional optical signals can introduce noise and other impairments that degrade quantum channels. Raman scattering, optical power levels, fiber attenuation and losses introduced by multiplexers and other optical components all require careful engineering.

Furthermore, conventional optical amplifiers cannot simply be used to amplify unknown quantum states because of the quantum no-cloning principle. Quantum repeaters, which are needed to extend quantum communications over longer distances without relying on conventional amplification, remain a significant technology-development challenge.

Consequently, sharing existing fiber infrastructure does not necessarily mean that quantum networks can use conventional carrier optical equipment, transmission systems and operational procedures without substantial modification.

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Can quantum networking become an economically viable extension of carrier optical networks?

This is arguably the most important commercial question surrounding Toshiba’s project.  The telecommunications industry has a long history of investing in promising optical networking technologies that did not achieve their anticipated commercial potential. During the 1998–2002 optical networking boom period, substantial investment went into photonic switching and all-optical networking. The vision was to eliminate repeated optical-electrical-optical (O-E-O) conversions, allowing data to remain in the optical domain throughout the network. That was supposed to usher in ultra-long-haul, repeater-less optical transmission. Photonic switches were expected to deliver enormous capacity improvements, reduce equipment complexity and lower network costs.

Despite considerable technical development and industry investment, all-optical switching did not become the dominant architecture envisioned by its proponents. Although optical circuit switches, MEMS-based photonic switches and ROADMs achieved commercial deployment in carrier networks, the broader vision of entirely photonic networking—with switching logic and control performed optically and without electronic processing—never became a commercially viable mainstream architecture.  Conventional optical transport networks instead evolved through improvements in WDM, coherent optics, optical amplification, electronic switching and increasingly sophisticated optical-electrical-optical interfaces.  The telecommunications industry ultimately favored hybrid optical-electronic networks.

Quantum networking could face a comparable commercialization problem. The ability to demonstrate quantum communication over existing fiber does not establish that a scalable, economically competitive carrier network can be built using conventional optical infrastructure.

There have been encouraging demonstrations of quantum and classical communications sharing the same fiber. For example, Toshiba and KDDI reported in March 2025 a demonstration carrying 33.4 Tbps of conventional data traffic alongside quantum key distribution (QKD) over an 80-kilometer fiber. This is an important proof of technical feasibility, but it does not establish the economics of a nationwide, multi-user quantum network.

There are also fundamental differences among quantum networking applications. QKD distributes cryptographic keys, while entanglement-based networking and distributed quantum computing require additional capabilities and substantially different performance characteristics. Success in multiplexing QKD with conventional traffic does not automatically demonstrate that geographically distributed quantum computers can be interconnected economically.

My assessment is that quantum networking is more likely, at least initially, to require specialized infrastructure and equipment than to become a straightforward extension of today’s carrier optical transport networks. Existing fiber may be reusable in selected applications, particularly metropolitan links and carefully engineered WDM deployments. But specialized quantum transmitters, detectors, synchronization systems, quantum memories, repeaters and associated control systems could impose substantial additional capital and operating expenses.

The economics become even more challenging when dedicated fiber, trusted intermediate nodes, environmental controls and specialized maintenance are required. Carrier operators will need to justify these costs against the actual revenue-generating applications and the alternatives available to customers.

The US and European quantum networking research communities have demonstrated that coexistence with conventional optical traffic is possible. Nevertheless, practical quantum repeaters, long-distance entanglement distribution, multi-vendor interoperability and scalable network management remain important obstacles.

It is therefore premature to assume that quantum networking will develop into a broadly deployed carrier service simply because existing fiber can be used in selected demonstrations.

The photonic switching experience of 1998–2002 is a useful cautionary precedent: technically impressive demonstrations and substantial R&D investment do not necessarily translate into commercially successful network architectures.

Toshiba’s quantum technology background:

The project builds on more than 25 years of Toshiba research and development in quantum technologies. The company recently introduced its Quantum-Safe Networking (QSN) Platform, designed to help organizations integrate quantum-safe protection into existing communications networks with reduced complexity, equipment footprint and cost.

It is important to distinguish these two technology areas. Quantum networking seeks to distribute quantum information and connect geographically separated quantum systems. Quantum-safe networking, by contrast, protects conventional communications against current and anticipated future cryptographic threats, including those posed by sufficiently powerful quantum computers.

Although related through their use of quantum technologies, these are distinct applications with different architectures, infrastructure requirements and deployment objectives.

Conclusions:

Toshiba’s collaboration with BT and Colt is a worthwhile technology-development effort addressing a genuine challenge: how to scale quantum networking without incurring the prohibitive cost of building entirely new fiber infrastructure.   However, the critical test is not whether quantum signals can coexist with conventional data traffic over selected fiber links. It is whether the complete quantum networking architecture—including its specialized optical components, repeaters, control systems, maintenance requirements and operating costs—can deliver sufficient commercial value to justify deployment by telecommunications operators.   Until that economic and technical case is demonstrated at meaningful scale, expectations for quantum networking as a natural extension of existing carrier optical infrastructure should remain guarded.

The historical lesson from the 1998–2002 photonic switching and all-optical networking boom is not that optical switching failed altogether. Rather, the ambitious vision of an entirely optical network, eliminating electronic switching and processing throughout the network, never materialized. Commercial optical switching did succeed, particularly at the wavelength and circuit layers, through technologies such as MEMS switches and reconfigurable optical add/drop multiplexers (ROADMs). However, electronic switching, processing and control remained essential components of commercial carrier networks. The industry ultimately adopted hybrid optical-electronic architectures rather than the fully photonic networks originally envisioned.

Quantum networking faces a similar commercialization challenge. Will it establish economically viable applications as a specialized extension of conventional optical networks, leveraging existing fiber wherever technically feasible? Or will its unique physical-layer requirements—including quantum repeaters, specialized transmitters and detectors, synchronization and stringent signal-management requirements—necessitate largely separate infrastructure with substantially higher deployment and operating costs? The ability to demonstrate quantum communications over existing fiber is encouraging, but does not establish that a scalable, commercially competitive carrier-network architecture is achievable. Ultimately, as with photonic switching, technical feasibility must translate into compelling economics and sustainable customer demand.

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