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Nobel Prize in Physics: Alain Aspect, a pioneer of the quantum revolution

And fifteen! Thanks to physics, France won its fifteenth Nobel Prize in this discipline (equalizing the number of Nobel Prize winners in literature) in the person of Alain Aspect, researcher at the Orsay Optical Institute (Essonne).

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Nobel Prize in Physics: Alain Aspect, a pioneer of the quantum revolution

And fifteen! Thanks to physics, France won its fifteenth Nobel Prize in this discipline (equalizing the number of Nobel Prize winners in literature) in the person of Alain Aspect, researcher at the Orsay Optical Institute (Essonne). This great specialist in optics and quantum mechanics is known worldwide for his work on quantum entanglement in 1982, namely the ability of two particles to exchange information, even at a distance from each other. The 75-year-old Frenchman was crowned with two colleagues, American John Clauser and Austrian Anton Zeilinger.

The "first age" of quantum physics goes back to the beginning of the 20th century when many researchers demonstrated that particles (electrons, protons, atoms, etc.) have a dual behavior thus explaining a large number of phenomena (such as stability of matter) and opening the way to numerous applications (transistors, lasers). Then, we spoke of "second quantum revolution" when other properties of quantum physics were revealed, in particular this famous concept of entanglement: two entangled objects form a single whole which contains more information than the sum of the properties. of the two objects. In computer science, this gave birth to the quantum computer in the 1980s (we no longer speak of binary bits but of qubits which, in theory, can take on an infinity of values) allowing man to hope one day to have of infinite computing power. But since the work of Alain Aspect and his colleagues, the quantum revolution has opened up many other perspectives - always in the infinitely small - as the Express had shown in January 2021 in the field of quantum sensors which could lead to new useful instruments for science.

The quantum computer allows man to dream of infinite computing power. A tool giving him the possibility of modeling everything: from complex climatic consequences to the smallest neurons of a brain. But in laboratories, we are also working on quantum sensors, extremely precise measuring tools, using the properties of atoms. Much less publicized, this branch of research could seem less noble. Yet it is vital and the most advanced. "With these devices of a new kind, we will probe the depths of the Earth, study the magnetic fields or guide machines with unequaled precision", warns Marko Erman, scientific director of the Thales group. According to him, a real metrology revolution is underway. And it won't be long before you see the effects, because the first models are already operational.

"This technology is reaching maturity. It must be said that many scientists have been working on it for several decades", confirms Alain Aspect, professor at the Institute of Optics Graduate School - University of Paris-Saclay, and at the Ecole polytechnique. Thus, at the top of Etna, in Sicily, the French start-up Muquans has already installed its so-called “cold atom” gravimeter. Seen from the outside, the object seems banal: it is a cylinder 70 centimeters high connected to a slightly larger block of metal filled with electronics. But inside, an astonishing process is at work: “A cloud of atoms is cooled there by laser, until it reaches a very low temperature (about one millionth of a degree above absolute zero). then makes it possible to calculate with great accuracy the gravity to which they are subjected", explains Arnaud Landragin, researcher at the CNRS, director of the Time-Space Reference Systems laboratory, and co-founder of the company. What will this information be used for?

"Before an earthquake, the tectonic plates deform slightly, which creates an increase in gravity above them", explains the scientist. Thanks to its quantum sensitivity, the sensor discerns minute variations in the earthquake. "We are not yet able to accurately predict earth tremors; no system currently allows it, insists Arnaud Landragin, but with this device, geophysicists will collect valuable information." And this is just one of the possible applications of this technology. In astronomy, scientists should better assess gravitational waves, those tiny vibrations produced by extreme phenomena, such as the merger of two black holes. A task that is already being tackled by teams from the Annecy laboratory for particle physics and the astroparticles and cosmology laboratory in Paris.

Measuring the speed and rotation of atoms will also improve the navigation of planes or boats, especially in the event of loss of GPS signal. "Today, to remedy the absence of this, an airplane relies on non-quantum elements: gyrometers and mechanical accelerometers. Except that these instruments 'drift' over time. For an airliner, for example For example, this results in an error of several hundred meters after an hour of flight. An atomic sensor would offer much more precise guidance", assures Marko Erman. To the point of being able to completely do without satellite tracking? "This technology has long been of interest to the military, in particular for precisely directing submarines at the bottom of the ocean", admits Alain Aspect. But for now, atomic inertial units can only be used in the laboratory. Very bulky, they still do not support vibrations, underlines a recent article from the CNRS.

However, researchers have other types of small, extremely promising quantum sensors, according to Alain Aspect: NV centers (from the English "nitrogen vacancy", "nitrogen vacancy center" in French). These diamond crystals made in the laboratory, in which the scientists come to house a nitrogen atom, are able to detect very weak magnetic fields if they are excited correctly using lasers. "Their main advantage is that they operate at room temperature. They therefore do not require heavy cryogenic equipment, like other systems", explains Marko Erman. This raises many hopes. In terms of health, for example, NV centers would be a means of studying the reactions of the human brain in detail. "We all emit electromagnetic waves. These are the signatures of our cognitive activity, even of our disorders. Already, with current techniques, doctors are making maps of our brain in activity. But with quantum, this will be like going from a blurred image to something very clear. This will help scientists to better understand neurodegenerative diseases, such as Alzheimer's or Parkinson's", promises Marko Erman.

The technologies developed for the sensors also pave the way for the creation of miniaturized equipment: a portable magnetic resonance imaging (MRI) machine, for example, or even smaller antennas intended to replace bulky models in the form of salad bowls. Of course, as in any revolution, one must be wary of false promises. Regularly, articles extol the merits of quantum radars. Devices for military use to see without being seen, and even to spot stealth aircraft. "I doubt the implementation, says Benjamin Huard, professor of physics at the Ecole Normale Supérieure in Lyon. In the atmosphere, particles emit a lot of radiation. These conditions actually limit the possibilities of using a quantum radar. . To the point that it is probably better to increase the power of normal radars"

Quantum sensors still offer many avenues of research. "We regularly complain about the deindustrialisation of the country, but with sensors, there are many opportunities for companies and start-ups to seize. In addition, France has a large pool of specialists", confirms Arnaud Landragin. "Of course, the quantum computer alone is likely to revolutionize many fields, but it may never see the light of day. Or it will be in a very long time. With sensors, we are sure to have concrete progress" , bluntly explains a researcher. The government got it right. In its latest plan in the quantum field, presented in December, the State reserves 250 million euros in funding over ten years for the sector. A sum that will certainly capture the attention of young people.

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