Serge Haroche

Serge Haroche is a physicist who was awarded the 2012 Nobel Prize for Physics jointly with David Wineland for “ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems”.

Haroche graduated from Ecole Normale Supérieure (ENS), receiving his doctorate in 1971. After a post-doctoral visit to Stanford University in the laboratory of Arthur Schawlow (1972-73), he became full professor at Paris VI University in 1975, a position he held until 2001, when he was appointed Professor at Collège de France (in the chair of quantum physics). Since 2015, he is professor emeritus in this institution.

Starting in the 1980s, Haroche has designed ingenious experiments to study quantum phenomena when matter and light interact. He has been able to capture photons using a trap made of highly reflecting mirrors between which the light particles can bounce billions of times. This device allowed Haroche and his team to study the photons by passing atoms through the trap.

Haroche has received many prizes and awards, including the Grand Prix Jean Ricard of the French Physical Society, the Einstein Prize for Laser science, the Humbold Award and the CNRS Gold Medal.


As told to Lan Anh Vu

Why I Pursued a Career in Physics

I have always loved science and math. I have been fascinated by the fact that nature obeys the laws of mathematics. The idea that we can have a grasp on the real world through mathematics has captivated me since I was a child. When the first rockets were launched into space, I was in high school and I could use my simple knowledge of Newton’s law to calculate the speed a satellite must achieve in order to orbit the Earth. This was fascinating!

When I entered Ecole Normale Superieure, I was quickly drawn to physics. I chose atomic physics because I was enthralled by the lectures given by a few charismatic professors, among whom Claude Cohen-Tannoudji stood out. He was doing breakthrough research in this area and had the gift to share his enthusiasm for physics and for the world of atoms with his students.



In my research, the challenge has been to realize experiments which have exhibited in a clear way the counter intuitive behavior of quantum particles. Their strangeness vanishes when they are perturbed by their environment, so that the direct observation of “text book” quantum effects is difficult. Realizing the perturbation-free “thought experiments” which the founding fathers of quantum physics had imagined has not been easy. It has required to develop a lot of technology with lasers, cryogenics and superconducting materials, as well as the invention of subtle ways to manipulate and control single atoms and photons.


Lessons Learned

One of the privileges of a scientist is being able to exchange ideas with the scientific community around the world, to interact with colleagues who have different backgrounds and cultures and yet share the same passion and curiosity for knowledge; another is being able to follow the intellectual paths which have led great scientists to their discoveries. Anyone can be fascinated by the works of artists like Leonardo da Vinci or Mozart, but it is much harder for a non-scientist to grasp the beauty of Newton’s or Einstein’s theories and to appreciate the depth and power of their thinking. The beauty is much more hidden in science than it is in art. As scientists, we have the privilege of understanding this elusive beauty. One of our duties is to try to unveil it to the general public through various media (books, movies, TV programs, internet, public lectures), by using proper images and metaphors. In this way, scientists could defuse the fear of science which often comes from the feeling that it carries an inaccessible and mysterious power.


How I Deal with Failure

Science especially experimental science – often proceeds by trials and errors and failure is an inherent part of the game. I have faced failures many times in my career. The first type of failure is trivial. The technology fails you. Sometimes a piece of equipment is accidentally destroyed by manipulation and then it has to be rebuilt, which means it may take months or even years to recover from a miscalculated experiment in the lab. The second kind of failure happens because you go in the wrong direction – you assume something would work in a certain way and you make an assumption which is not right, and then you have to backtrack and do it differently. How to cope with failure? You have to be persistent and not lose faith in your ability to reach your goals. In these circumstances, it greatly helps to work with a group of colleagues who share the disappointment of failures as well as the exhilaration of successes. I’ve been lucky enough to work with such a team throughout my career.


Quantum Physics

Quantum physics is the theory which explains how nature behaves at the atomic level. At this microscopic scale, the laws of physics are counter-intuitive. An atom or a photon can be in different positions or different energy states at the same time, in what is called a “state superposition”, a situation which is never encountered in macroscopic objects. Taking state superposition into account is essential to explain at a deep level the laws of chemistry, of electricity, of nuclear forces, and of optics. In my research, I have tried to elucidate how the quantum laws are involved in the most elementary processes of optics, when single atoms interact with single photons. This is basic science, driven by mere curiosity. But the knowledge acquired in this blue sky research might one day lead to new applications and new devices. Our understanding of the quantum laws has already resulted in many powerful technologies invented in the 20th century, such as the laser, the atomic clocks and the GPS. In a similar way, our ability to work with single quantum particles may lead in the future to new devices directly exploiting the quantum logic to compute, communicate or measure better.


Manipulation of Individuals Quantum Systems

My team and I trapped photons in a box, and manipulated and controlled these grains of light to try to understand the deep property of quantum system and maybe to find a way to use this property to do something useful.

Photons, which are waves and particles at the same time (a consequence of the superposition principle), are very elusive and fragile when you try to control and manipulate them. Photons are in fact all around us. When you look at an object illuminated by a source of light, the photons it scatters enter your eye and are destroyed on your retina, as they generate the nervous signal sent to your brain. We needed to study the photons in a more gentle way, so as to not destroy them by the very act of observing them. We thus developed a non-destructive procedure to detect them, by which we could keep studying them and learning as much about them as possible. Our solution was to have them trapped in a box made of mirrors facing each other, which kept them bouncing between the walls for a long time. We then sent atoms passing between the mirrors which interacted with the photons without absorbing them. By detecting the atoms after they had left the box, we got subtle information about the photons and were able in this way to directly demonstrate the strange ways in which matter interact with light at the quantum level.


Problems Facing Science

Science is an essential activity in a civilized society. It is a source of knowledge which satisfies the innate curiosity of mankind. It is also the source of powerful tools, medicines and technologies which have made our lives longer and better. In order to face the challenges ahead of us (climate change, need for renewable energies…), more innovations are required and we thus need more minds to take part in science. For that, we need to have a strong education system. Young students who are eager to learn should be able to develop their curiosity and creativity. In order to nurture these qualities, you need a free society, which values freedom of speech, freedom of thought and freedom of circulation. These values are now endangered, notably by the spread of populism. Conspiracy theories which, for instance, deny the climate change or the usefulness of vaccination, pervert the spirit and values of science. They flourish on the internet and endanger the very notion of truth, which is at the heart of the scientific process. The emergence of the “alternative facts” trend and the confusion between baseless opinions such as creationism and scientific theories founded on facts illustrate this sad state of affairs. All scientists worry about this evolution. Let us hope that our societies will have the strength to resist it and to keep alive the values of enlightenment.


Advice for Aspiring Scientists

Firstly, you need to have a passion for science, because it is a very competitive, difficult and demanding field. And your passion will hopefully help you keep an optimistic view of the future, with the firm belief that science will overcome the problems I just mentioned.

Secondly, you should choose a field and a research topic that you feel fascinated and excited by – and this often requires luck. In my case, I chose my particular research area by chance, because I happened to be exposed to an enthusiastic teacher and the success of my research has been due to the quality of the people I have had the fortune of working with. In the scientific process itself, luck is also an important factor and you should learn how to recognize it. Sometimes, things happen that you did not expect – either by accident or because some feature of an observation may have surprised you by showing you something new. You have to recognize and harness luck and not miss the opportunities which are presented to you by it.

Finally, do not get discouraged by the amount of things you have to learn. As one of my mentors once told me, in order to be successful in a specific area, you need not know everything. After all, what you are expected to do is to discover just one thing that nobody has known before. This is more easily said than done of course, but it helps not to be overwhelmed and inhibited by all that you don’t know. This does not mean of course that the knowledge accumulated by your predecessors is useless. It is essential, but without mastering it all, you can often learn about it by interacting with other scientists and get good advice from them. In this respect, again, you should be lucky to work in the right environment.