And the light will be: Yves Caudano's ambitious goal

As sophisticated as our computers are, they're still based on the same technology: information is conveyed by the electron, whose presence corresponds to the number 1, and whose absence to 0. This basic unit is called the bit.

There is, however, another way of encoding information. In fact, it's possible to exploit the particular properties of particles on a microscopic scale, and which are defined by quantum mechanics. Using photons, for example, the particles that make up light, quantum technology would then be based on qubits, far richer than conventional bits. Such a change would pave the way for quantum communications, such as cryptography, and quantum metrology, which enables physical quantities such as time to be measured with very high precision.

However, isolating photons remains an infinitely complex task today."With a light source like a light bulb, millions of billions of photons are emitted at the same time, reveals Yves Caudano, FNRS-qualified researcher and lecturer in physics at UNamur.

To this end, the scientists plan to synthesize new molecules capable of emitting single photons. "These molecules will be associated with complex metallic nanostructures, which will aim both to make these sources reliable, i.e. capable of emitting photons on demand, but also to ensure that the photons will always be sent in the same direction", says the physicist. "One of the challenges of this project is also to produce photon pairs, by arranging these molecules in crystals and thus creating particular optical conditions."

These pairs of photons, also known as entangled photons, are one of the quantum properties of particles on which systems such as quantum cryptography are based.

Thus, a quantum cryptography algorithm would be able to solve problems in record time. "Actually, the cryptography that protects our communications relies on the complexity of a calculation, which no known algorithm can solve in a sufficiently short time," he summarizes. In contrast, there is a quantum algorithm that has been shown to be capable of performing this calculation in a reasonable time. And so, for example, decode all current messages encoded in this way."

To succeed, Artémis relies on the expertise of 10 European institutions, and a budget of over 3 million euros. Yves Caudano, as a quantum physicist, is particularly involved in the quantum characterization of photons. "We will create experiments to ensure that molecules do indeed emit single photons", he states. "Then we'll look at the photon pairs emitted, to determine all their characteristics."

These measurements are a crucial aspect of the project, as they are what will show that photon sources are reliable, and usable by technological systems outside a laboratory. But as with everything to do with quantum physics, the difficulties here are singular. "In classical physics, the system we are studying is independent of its observer", he explains. "Or, in quantum mechanics, any measurement also destroys the state we seek to observe."

So we'll have to be cunning. Yet Yves Caudano is precisely a specialist in what are known as weak measurements, capable of only slightly disturbing the system under study. They must, however, be carried out a large number of times to obtain usable information. "Thanks to a new technique, we've found that these weak measurements also enable us to amplify extremely weak phenomena, which we couldn't see before. This will be extremely useful to us in the design of quantum experiment protocols intended to show the efficiency of light sources."

The project, which will run until 2027, is still in its early stages, and the first molecules are only just emerging from the laboratories. Considered a high-risk project, it should enable the EU to become a leader in the quantum computer race.

Thibaut Grandjean