Interview with the 2022 Nobel Prize laureate in physics Alain Aspect on 6 December 2022 during the Nobel Week in Stockholm, Sweden.

Where does your passion for science come from?

Alain Aspect: When I was a kid, I lived in a small village in France. At that time it was very rural, so there were not so many technical objects, but I was fascinated by any tool from the carpenter, from people like that. I don’t know why, but I was really always fascinated by technical objects. Then I was a reader of Jules Verne. Jules Verne is an inspiration or more, it was confirming what we were learning. Remember it was in the fifties and the sixties, it was after the war, and there were the ideas of progress. There is one book of Jules Verne L’Île mystérieuse, ‘The mysterious island’, where engineers and scientists arrive on an isolated island, and because they have the knowledge of science and technology, they will be able to develop a comfortable civilisation. That was a belief that science is good for humankind.

Are you still a reader?

Alain Aspect: Oh, yes. Sometimes, for the pleasure, I go into one of these old books.

What made you decide to pursue science?

Alain Aspect: I think really since elementary school, I was attracted towards scientific “things”, because at elementary school it’s very simple. Anytime the teacher was doing a little “experiment”, I was always interested by that. Then I went to high school, and it turned out that at that time, for four years in high school, there was math, and natural science, biology, but there was nothing about physics and chemistry for four years, and I felt frustrated. I was waiting for the moment when I would learn physics and chemistry, so I think I was always fascinated by it. What happened then? In the last year of high school, I had a fantastic teacher at the high school who really determined my life, because he taught me what is the approach of physics. That is to say a blend between pragmatism, but also solid mathematical model, and at each time finding the simplest possible model, but anyway, it must be sophisticated enough to render an account of the phenomena. This is really a high school teacher who taught me that.

When did you know you wanted to pursue quantum mechanics?

Alain Aspect: Well, I smiled because the story is interesting. I had excellent studies, excellent courses at university except for quantum physics. Seeing it from now, clearly it was a very bad teaching. The professor did not understand what was really quantum physics. I had that frustration, I knew that it was important, and I knew that I did not know it well. What happened that while I was in Africa, in Cameroon, for military service – okay, I was teaching rather than going to the army – I had the opportunity to buy a book by Claude Cohen-Tannoudji, Nobel Laureate in 1997, Bernard Diu and Frank Laloe, and I learned quantum physics into that book, and then I understood what it was about. When I came back to France and found a paper by John Bell, which determines our experiments, I was ready to appreciate the paper by John Bell.

What does it take to proceed in science without support from others?

Alain Aspect: When you are teaching, it’s a different world, so for me, the week was cut in two parts. There was the part dedicated to building that experiment and making tests and progressing in the development of the experiment that I was doing. On the other hand, there was teaching. Teaching is very rewarding because if you feel that the students understand what you are explaining, that they’re making progress, really it makes you happy. I think the fact that I was teaching was crucial for me. Teachers are very important. I mean, the fact that we have a future scientist depends on teacher and elementary school teachers, high school teachers.

What advice would you give to a student interested in science?

Alain Aspect: More generally, my advice would be follow your taste. Don’t listen to fashion, because maybe nowadays they tell you that this is a fashionable subject, but five years from now, it’ll be another one, so I think you should really work in what you are interested. It may be basic science, it may be technology. It must be application – it just depends on the person. Each person is able to know exactly what is his or her passion, and this is what they should follow.

How do you like to spend your free time?

Alain Aspect: What can I say? It depends on the moment in my life. When I was younger, I was spending a lot of time in sport, hiking, playing tennis, etc. When you get old you are not as fitted for doing so much sport, so what do I do? Cooking, I like cooking. I also like rehearsing for magic tricks. Since I got mandatory retirement I thought I had some free time, and I started learning to do magic with cards. I’m not an excellent magician, I know some classical tricks, but when I do these tricks, rather than saying the usual words of a magician, I pretend that it is quantum. So, when a car jumps from here to my hand, I say, Oh, this quantum tunneling effect. I spend some time doing that, and of course, spending time with the family, my wife, grandchildren, my children.

Are there any similarities between quantum physics and magic tricks?

Alain Aspect: Not at all. Because magic tricks, really if you want to do well a magic trick, it has to become automatic, like riding a bicycle. Your fingers work independently of you, and then you can think about a speech, which has nothing to do with what you are doing. You can pretend that it is quantum physics because your fingers work without thinking of them. It’s certainly not like an experiment, because in an experiment, each time you turn a knob, you have to think about what you are doing, and observe and react.

What environments help with creativity?

Alain Aspect: I need to have apparatus and knobs to turn. So, for instance when I cook, there is something which is very special, l’oeuf parfait, perfect egg. It has to be cooked at 64 ºC, not 62, not 66. I like to have a thermometer and to tune the heating, etc. Probably it reminds me of doing an experiment, adjusting everything in real time – observing, reacting, tuning.

Can you tell us about the object that you are donating to the Nobel Prize Museum?

Alain Aspect: The original thing in my experiment is the fact that the experiment is about two photons traveling to detectors. The idea is to change the setting of the detector while the photons are traveling. This takes only one or two dozen of nanoseconds, so it has to be very fast, and you cannot rotate an object in a few nanoseconds. My idea was to have a switch, and the switch would send the light either towards a first apparatus or towards a second apparatus. If the switch was fast enough it would be equivalent to a single apparatus operators rotating from one position to the other one, etc. These was my initial idea, I had published it from the beginning, and a company had promised to deliver the switch. In fact, the switch was my idea. It was based on the interaction of light with an acoustic standing wave. A company had promised to deliver it, but I wanted it big enough. After some time the company said, We cannot deliver it because so big we cannot we cannot make it, it’s too big. The reason was that when there were sticking a transducer on a crystal, it has to be done at high temperature, and then because a dilation is different between the material, it was breaking all the time. The problem was a contact between the material and the transducer. I was in despair because I needed that. I began to think, and when you are despaired, you become creative. Suddenly I realised that I did not need a crystal, water turns out to be a good material for that. If I have transducers in water, no problem of different dilation, there will be no breaking, so we built homemade – and the object I come is really homemade – it’s like, I don’t know how you say, in French a bricolage, one thing which is not a nice object, but it worked!

What about the future of quantum mechanics excites you?

Alain Aspect: In fact, what is exciting in the last, say decade or decades, is the fact that smart people discovered that entanglement can be used for applications and this whole world of quantum technologies. The idea that maybe we have a quantum computer or quantum simulator, which is able to solve problems that we don’t know how to solve with our usual computers. I think this is very exciting because when you have been working in fundamental science and suddenly somebody comes and say, You know, your pair of entangled photons can be useful for something, I like this idea. This idea of quantum computer, I think that they can be fantastic. We have problems of optimisation, for instance, now we have wind electricity, solar electricity, and the equilibration of the electric grid is a very complicated problem. It’s so complicated that you cannot find the solution with a standard computer because it’s called a difficult problem, a problem for which the time of computing increases exponentially with a number of elements to adjust. It may well be that quantum computers can help solve this kind of problem. Not only this one of course, but this kind of problem. To be honest, I would be excited to see that.

Do you ever think about your professional legacy?

Alain Aspect: Oh no, but I can think about it. I think that if there is something I would like to teach is curiosity. When something interests you, just go into it and try to understand better and better. Don’t listen to people who tell you it’s not interesting. If you find it interesting, just continue in it.

What do you think about people saying that you proved Einstein wrong?

Alain Aspect: Often people say that my experiment showed Einstein wrong. I think it’s not fair at all, because what happened is that Einstein raised a problem and his vision of the world was such that he came to the conclusion that one must complete quantum theory and Niels Bohr disagreed with him. The experiments we have been doing in test of Bell’s inequality show that quantum mechanics cannot be completed along the lines that probably Einstein had in mind. From this point of view, it’s true that he was not fully right, but he did not know about our experiments. In his time he could think that his interpretation was compatible with standard physics, so we don’t know what he would’ve said. Moreover, I told you that entanglement is a very important property who put the finger on entanglement and said, Ah, this is really amazing. It is Einstein. So, when people say, Oh, you showed Einstein wrong, I say, Come on, I showed Einstein was great, and if he had known what we have today, nobody knows what he would’ve said.

Watch the interview

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