Introduction
A telecommunications system ideally achieves a good level of protection of the transmission against espionage. Quantum information technologies are likely to improve the performance of existing systems in this respect. Quantum telecommunications, based on the mastery of technologies based in particular on quantum entanglement, significantly impact the field of cryptography. They require the development of new infrastructures, which will eventually form a quantum Internet.
Post-quantum cryptography
We often talk about the upheaval that the arrival of operational quantum computers would cause in cryptographic standards. Quantum algorithms would very quickly overcome all existing defenses: on condition that quantum computers of sufficient size to run, in particular, a prime number factorization algorithm is available. This is not currently the case, but it is a scenario to be taken into account when developing post-quantum cryptography.
The sharing of quantum keys
Quantum technologies have other highly disruptive short-term ramifications for the current status quo in telecommunications. The technology best mastered is that of quantum key sharing. The principle consists of operating the same protocol to measure the polarization of two entangled photons, spatially distant. The result of the measurement, which cannot be known in advance, is the same in both places and can be used as a cryptographic key. Even better, any interception will be easy to detect. In principle, the sharing of quantum keys makes it impossible to spy on a target without the target knowing it. A major breakthrough, in itself. In particular, we know that long-distance sharing was carried out between China and Austria in 2016. However, this technique requires high-quality optic fiber infrastructures. Several R&D organizations are currently exploring ways to put entanglement at the service of cryptography in a more efficient way.
The Quantum Internet
Sending qubits over long distances is to be distinguished from the key sharing mentioned above. The idea is to link quantum processors and equip them with quantum memory. In order to make maximum use of the existing communication infrastructure, optical switches capable of providing qubits to a given quantum processor are required. These switches must preserve quantum coherence, which makes them more difficult to achieve than standard optical switches. Quantum repeaters are also needed to transport the qubits over long distances since classical signal amplification is not possible (qubits cannot be copied).
Conclusion: The quantum shift in telecommunications security seems inexorable
What are the impacts for the future that really need to be taken into account in quantum telecommunications? The question refers to a double uncertainty: technological and strategic. Because the owner of these technologies will not spontaneously reveal its advantage to other players… a situation that is conducive to triggering a technological race that unfortunately has the potential to be both vain and ruinous for everyone. Nevertheless, it seems clear that cryptography is the most mature field of quantum information technology, and that the expected advances in this field will have a major disruptive effect. There will be a before and after of quantum encryption for strategic players familiar with the discipline of secret communications. When exactly, and with what precise technologies, is the question that arises in terms of our customers‘ industrial roadmaps!
