• French quantum technology consortium shows there’s more than one way to skin Schrödinger's Cat 
• One experimental quantum communications network uses existing but slightly adapted commercial fibre-optic infrastructure to distribute quantum keys
• The other uses co-propagation techniques in a wave division multiplexing (WDM) connection using deployed fibres

In France, the ParisRegionQCI (Quantum Communication Infrastructure) consortium has just finished the construction of a trial quantum communication network that operates over existing fibre optic infrastructure.

The QCI is led by Orange, the French multinational telco and, it is claimed, the new experimental network is proof-positive that it is possible to provide ultra-secure quantum communications based on tried-and-tested terrestrial, globally deployed commercial-quality fibre optic technology. Details of the achievement are contained in an updated blog on Hello Future, Orange’s research and innovation website.

In addition to Orange, another French member of the QCI consortium is the Thales Group, the multinational corporation with interests in aerospace, defence, transport, security and electronics. They are joined by giant Finnish vendor Nokia and a variety of startup companies, including Quellela, VeriQloud, KETS Quantum and CryptoNext, with additional input coming from academics and university research teams. 

During work on the trial quantum communications system, emphasis has been on taking a hybrid approach to its development in the hope of realising a viable model applicable to the large-scale, multi-user quantum networks of the future. 

The ultimate goal, as per the overarching European Quantum Communication Infrastructure (EuroQCI) programme, is to construct a fully secure quantum comms network to cover the entirety of the European Union (EU) and all its overseas territories. That is an enormous area and the project will be feasible only if the cost is kept down to manageable levels, and that will mean using extant fibre optic cabling to carry the quantum data traffic. 

As Thomas Rivera, an Optics PhD and a lead research scientist at Orange, explains in the Hello Future blog, “Quantum communications equipment is very expensive. To secure a link of less than 100km on a dedicated fibre, it takes approximately €180,000 to €250,000 just for a QKD [quantum key distribution] system and the financial equation quickly becomes insoluble. Thus, as part of the project, we took the gamble of banking on existing installations. We started with classic fibres already deployed by Orange France, some active and others dormant.” 

He adds, “We have slightly adapted and qualified these fibres in terms of quality and performance to see how we can achieve the prerequisites of quantum communication for the purpose of transmitting QKD. In short, this involves taking measurements of the optical losses by sending packets of photons into the fibre and characterising their roundtrips. Then, we deployed a quantum communication system in the field that was developed by ID Quantique. We defined a seamless network architecture, added a layer of services, and implemented an encryption system adapted by Thales to accept these new quantum-generated keys.” 

Here, the network given over to the exchange of keys guarantees their transmission between two devices – that on which the data is being encrypted and, on the other, that on which it is being decrypted. The encryption key is generated using a quantum random number generator (QRNG). 

QKD is a communications method that implements a cryptographic protocol involving components of quantum mechanics: It enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt messages.

The exchange of cryptographic keys is a provable guarantee of the security integrity of a message. This is because, in a quantum system, it is impossible to create identical copies of an unknown quantum state. This stops would-be cyberattackers from copying the data. 

Simultaneously, any outsider attempting to intercept and capture such data disturbs the quantum system and instantaneously alerts the legitimate senders and recipients of an incursion while deleting the communication itself, such that it has not been sent in the first place.

Experimental system will be kept and eventually become part of a wider quantum network

To date, the quantum fibre network built has a range of 80km and interconnects a number of partner quantum nodes from the the Plateau de Saclay (Thales, Institut d’Optique, Télécom Paris) to the Sorbonne University LIP6 laboratory in central Paris, via the Orange Gardens site in Châtillon. QKD was set up on the fibre infrastructure backbone with relays secured by post-quantum cryptography (PQC) to cover an extended distance range in Orange’s fibre optic network. (PQC is the next generation of public key cryptography which is resistant to quantum computer attacks.)

The installed solution combines IDQ’s commercial Cerberis XG QKD system with an embedded key management system (Clarion KX software suite), CryptoNext’s Quantum Safe Library (C-QSL) and classical symmetric cryptography, noted IDQ. In the experimental network, QKD provides unbreakable key exchange between remote encryption systems, while PQC guarantees relay security in large-scale QKD network deployment. The infrastructure will now become part of a network that extends beyond the Paris region.

Quantum comms options

But this isn’t Orange’s only quantum communications effort, as the telco has been adding another string to its quantum bow. At its research base in Lannion, Brittany (in northwestern France), Orange is also experimenting with ico-propagation techniques for the transmission of encryption keys. 

According to Ribera, the technique uses a single mode fibre to carry both the quantum signal dedicated to the key and the “conventional” signal associated with the message data, that is to say, the wavelength division multiplexing (WDM) data stream.

He explains: “The quantum channel can thus be added to existing infrastructures, at a different wavelength from the WDM channels already deployed, avoiding excessively heavy investments, in addition to those linked to QKD equipment.” 

This complementary approach is an integral part of the QCI project that continues to examine network infrastructure techniques and technologies that have already been commercially deployed rather than relying on expensive dictated fibres.

- Martyn Warwick, Editor in Chief, TelecomTV