Segre Haroche, 77, says he felt the need to look back at the end of his career. He led the team of physicists who in Paris were able to measure light, literally, by trapping it in a box, this earned him the Nobel Prize in Physics in 2012. La Sapienza chose him to hold the cycle of lectures of the Enrico chair. Fermi, entrusted every year to one of the leading international scholars who have contributed significantly to specific research fields. To tell the light, he who places himself a little at the end of the story, started all over again, starting right from Italy and Galileo, to get to quantum computers. In his lectures15 in all, from 27 January to 12 May, also online on Zoom, explained to everyone, not just students and colleagues, the wonders of research that have led to the technological revolutions of recent decades.
He arrived in Rome a few months after the Nobel Prize in Physics to Giorgio Parisi. What do you think?
“I was very happy. I think it is a nice recognition for what La Sapienza and Italy have done for science in general in modern times. In my classroom there are large photographs of Amaldi, Fermi, and even Galileo. But I think that countries like Italy and France are not investing enough in research and basic science and I’m sure Giorgio Parisi has highlighted it “.
Where does the science of light begin to be told?
“When people began to ask profound questions about the nature of light, it is the period in which modern science was born. The seventeenth century was the century of Galileo and Newton. They led to the modern scientific method, observation, experiments, theory and prediction of new effects. It is the virtuous circle between experiments and theory that have gone on together ever since. In the nineteenth century, new questions led to the theory of relativity and quantum physics. The profound questions about light were the point of departure of the theories that have revolutionized our lives, not only because they have led to a better understanding, but also because they have led to new tools, new devices, such as lasers.I started my career when they were just invented 60 years ago. An extraordinary technology “.
What do light and gravity represent for modern science?
“Light and gravity are the first things a child notices, gravity because things fall, and light because it is thanks to it that we relate to the world. What is incredible is that we do not yet fully understand them, they are there. still gap between the deep levels of quantum physics and general relativity. Modern research is moving towards combining these two aspects “.
What has the light taught us in understanding the world?
“On a deep level it taught us that space and time are mixed together, it is impossible to consider the three dimensions of space separated by time, so that we live in a four-dimensional space. And that when you add gravity to the problem, space becomes curved and light then propagates along curved lines. But this was only understood a century ago. Before there were other questions. Light taught us that electricity and magnetism are closely related and that light is a wave electromagnetic. This led to their unification, 150 years ago, with Maxwell. Using light, once it was understood that its speed is finite, it was possible to measure the size of the Universe “.
What are, in your opinion, the great insights into the history of the science of light?
“I think one of the great insights was that of Pierre de Fermat, a 17th century scientist, at the time of Descartes and Pascal. He said that light propagates on a line that takes the shortest time from one point to another, so in a straight line. But if it goes from air to water, it bends because it “prefers” to go through the air, where it is faster. It was a great intuition: to assume that light travels slower in water than in air. another gentleman who had a fantastic intuition of course was Einstein who based the whole theory of Relativity on the fact that the speed of light is the same for everyone. But to tell the truth, the intuition of relativity derives from Galileo, who had it not for light but for the mechanics of bodies If you are on a ship (traveling at a constant speed ndr) you have no way of knowing if it is you who are moving, because the experiments do not tell you “.
Difficult, counterintuitive concepts, from relativity to quantum physics, how are they told to a non-specialist public?
“You have to use metaphors, similarities with better known phenomena, that people might know. To understand Relativity you have to describe simple experiments, which give counterintuitive results but you have to prove that they are true. For example, what is called the” twin paradox “, a twin who leaves and comes back younger than the one left on Earth. In Einstein’s time it was difficult to make him understand. Now we do experiments every day that prove this to be true. The atomic clocks of GPS systems around the Earth go slower for this effect. And if this were not taken into account, the GPS would not work “.
We come to the studies that earned her the Nobel. Have you ‘touched’ the light?
“The paradox of light is that, when you see it, that light is dead because the photons are destroyed when you receive the information, transformed into the chemical reaction in your eyes. What we were able to do in Paris with my team was to detect the light without destroying it, measuring the same photon again and again and this could have interesting applications for quantum information “.
There has been a lot of talk about applications on quantum supercomputers based on your research, do you see progress ten years after the Nobel Prize?
“The fact that a quantum system can be in several states at the same time, in a superposition, means different realities, which brings us to Schrödinger’s famous cat metaphor. What we have achieved in the laboratory are small versions of this system. If we were able to do so. to use this phenomenon on a large scale we would be able to obtain calculations much faster than an ordinary computer, but the difficulties are many, one of them is decoherence, the fact that these quantum systems are very fragile and lose these properties very quickly. We have been working on this for ten years, I’m not very sure if we can build a quantum computer for practical use in the near future.
On the other hand there are other systems such as quantum simulators, made of a few tens of atoms or particles, which can be useful for example to obtain superconductivity at high temperatures, or to synthesize new molecules to produce new drugs. And use these counterintuitive properties for encrypted communications, quantum cryptography. You can also make systems sensitive to very small perturbations, probes that can measure magnetic fields or gravity with greater sensitivity. This is the new quantum technologyour research was one of the starting points “.
For which applications?
“If he had asked Einstein a hundred years ago what the applications of Relativity would have been, he would never have been able to predict the GPS. Or the laser. The people who made the greatest discoveries were unaware of the applications, and they never exaggerated with the predictions. . I think I’ll follow their example. “
Yet quantum computers seem to be one step away. It is not so?
“Maybe one day there will be one of these computers but it will have to be kept protected in a structure, possible only in some places in the world. It will never be a laptop, but maybe I’m wrong. It tells the story of the director of IBM who over the years ’40 argued that there would be room for at most five computers worldwide. “
The chair at Sapienza for which he will hold his lectures is named after Enrico Fermi. Scientific discoveries on light have led to great technologies but also to the construction of weapons, the most powerful, such as the atomic one. Do you think humanity is more mature now than it was a few decades ago?
“I don’t think humanity is more mature. When you have the power, that can be used to build weapons. Einstein was a pacifist, nevertheless he signed the letter to Roosevelt which started the Manhattan project because it was important at the time that allied forces were stronger than the Nazis. But science is not good or bad, it is what you do with it that is good or bad. For example, those who reject research on genetically modified organisms or mRna vaccines, because “they are not natural”, are wrong . You must acquire knowledge and then decide how to use it. You can never stop humanity from being curious and knowing. Fermi, Curie, the physicists of the last century were curious to understand nature and they did, they opened a kind of Pandora’s box. What we have said about weapons may also be true of the Industrial Revolution. We have been using oil and gas for more than a decade and now we are in danger from the climate and this is also an effect of science ” .
He doesn’t look optimistic
“I think we need to understand what real progress is and we need to steer science in the direction of the problems we need to solve. And so we need more research and resources. We need to find a replacement for fossil fuels. I think we need nuclear, because we will never have enough electricity to replace fuel-driven cars with electric ones. The sun isn’t always there and the wind doesn’t always blow. But to discuss all this, I notice that it is done not on the basis of science but on the basis of ideologies. I’m not optimistic because I see that many do not look at problems in a rational way, the development of fake news and conspiracy theories go in the opposite direction “.