Why space matters for QKD

Quantum mechanics means that QKD is inherently protected from eavesdropping. A quantum state encoded on a photon cannot be measured without disturbing it, thereby revealing the presence of an eavesdropper and invalidating the key. Furthermore, the no-cloning theorem of quantum mechanics means that quantum keys cannot be duplicated without similarly disturbing the initial state.

While quantum keys can be distributed using fibre-optic links, the distances over which this can be done are generally limited to hundreds of kilometres. Over larger distances, growing signal losses within the fibre-optic cables mean QKD is impractical for long-distance secure communication.

Transmitting quantum keys in space is therefore seen as a promising possibility for circumventing the limitations of fibre-optic cables. While there are several technical challenges in doing so, China’s Micius satellite proved the concept in 2017, distributing quantum-encoded photons to ground stations over 1,200 kilometres apart.

The European Space Agency’s EAGLE-1 mission is now set to become Europe’s first demonstration of a space-based QKD system, with launch expected in late 2026 or early 2027 at the time of publication. This is a significant step for the European Quantum Communication Infrastructure (EuroQCI) initiative, which aims to build a sovereign, quantum-secure communications network across the European Union.

Jurisdiction

Outer space is famously not subject to national appropriation. Article II of the Outer Space Treaty makes clear that no state can claim sovereignty over any part of it. Article VIII, however, provides that a state retains jurisdiction and control over any object it registers under the 1975 Registration Convention, even once in outer space.

Therefore, it is generally accepted that any satellite used in space-based QKD is subject to the national laws, including intellectual property laws, of the state to which the satellite is registered. While this is straightforward for a satellite registered by a single state, missions such as EAGLE-1, involving collaboration between multiple different states, can raise practical questions over which intellectual property laws apply.

What can be protected

QKD can be implemented using a number of different protocols. The protocols themselves are essentially mathematical methods and are therefore excluded from patentability as such under Article 52(2) and (3) EPC. However, new QKD protocols can be protected by directing patent claims towards a technical arrangement built around such a new protocol. Therefore, while a new protocol is by itself not patentable, a satellite which uses the new protocol to generate and distribute quantum keys is in principle patentable.

Space-based QKD can also be protected beyond technical implementations of new protocols. New satellite or ground-station hardware which more generally enables long-distance QKD, such as single-photon sources and detectors, filtering, timing, and modulation systems, is patentable, provided it is new and involves an inventive step.

Software for space-based QKD is also potentially patentable. While Article 52(2) and (3) EPC prohibits patents for programs for computers as such, this is not true if the invention provides a technical contribution beyond the underlying computer program. Software that controls a technical system, such as a QKD satellite or ground receiver station, provides such a technical contribution and is therefore patentable. Accordingly, software which handles scheduling, tracking, and handover is also patentable, provided it is new and involves an inventive step.

Space-based QKD therefore involves a wide range of technologies that are potentially patentable, from the underlying hardware through to the software controlling it. Protecting these innovations early is essential to allow free discussions with investors, prevent copying from competitors, and preserve commercial advantage.

Patent protection as the field develops

In the last 10 years, satellite-based QKD has moved from proof of concept to near-term infrastructure, and EAGLE-1 will mark a significant step for European capability in this area. For innovators, a patent strategy that considers hardware, protocol and software contributions will be essential to securing meaningful protection as the field develops.