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"We managed to break the mental fixation"

Interview with research professor Moti Segev, Faculty of Physics "Discovering a new, unexpected or counterintuitive phenomenon - these are the moments that motivate me." says Professor Segev 

Prof. Moti Segev in the laboratory. Photo: Technion spokespeople
Prof. Moti Segev in the laboratory. Photo: Technion spokespeople

At the end of the conversation with research professor Moti Segev, there is no doubt that this is a researcher who loves new experiments - not only mountains and glaciers like the one seen in the picture, but also new ideas and experiments in science. Segev, one of the five distinguished professors (Distinguished Professors) at the Technion, took a short break from his adventurous hobbies (and his research at the Technion) to give the opening lecture at the most important conference on lasers and electro-optics, which took place in early May in Baltimore. Segev, who has won many awards, including the prestigious quantum electronics award (the most important European award in the field of optics and lasers), and the prestigious Max Born award given by the Optical Society of America (OSA), talked with us about his extensive interests and achievements, and contributed some advice to young researchers and students entering this field.


What is the highlight of your career?
The peak was in Victoria, Canada, in 1988, at the end of the OSA conference on nonlinear waves, when it was clear that my work in the field of solitons had resonated. In the beginning, my ideas in this direction received many attacks. Papers have been published claiming that such solitons cannot exist. Others argued that these solitons are unstable and cannot be observed experimentally.
For a long time people simply did not believe, despite the fact that we published several theoretical and experimental articles in leading journals. People tend to mental fixation and walking in a rut. It is very difficult to change ways of thinking, especially when you are attacked by very senior scientists. But some good friends supported me all the way: Amnon Yariv from the California Institute of Technology, Steve Harris from Stanford University, Steve Forrest and Paul Prosnell from Princeton, and at some critical moments also Nobel laureate Nicholas Blumbergen. I also gained three very good friends who walked this difficult path with me: Bruno Crosignani, Greg Selmo and Dimitri Christodoulides. I believe that together we created a revolution in the study of solitons. So if we go back to that conference in Victoria in 1998, when dozens of groups continued our research, we realized that we had won: we had managed to break the mental fixation of a large community in science.

What are solitons?
Solitons are "wave packets" that are trapped within themselves and thus maintain a fixed configuration. The single soliton behaves, also in its relations with other solitons, as if it were a particle. Solitons can attract or repel each other, like two charged bodies, as well as become trapped in a spiral orbit around each other.
Solitons appear in a variety of systems, from liquids to plasma, acoustic waves on DNA molecules, sound waves in superfluids, elementary excitations in string theory, and gravitational phenomena in black holes. Solitons are found in many places and in many fields. Over the past 20 years, optical solitons—beams of light that behave as if they were particles—have become the leading research direction in all of soliton and nonlinear wave science.
Largely following your discoveries.
Indeed, I have been studying optical solitons since 1991, and over the years we have made many surprising discoveries. The most important among them, I think, is the discovery of the non-coherent solitons: solitons made of white light originating from an incandescent bulb. Imagine a simple light bulb, we focus part of its light into a beam 10 microns wide (a beam 10 times thinner than a hair), and direct it into a non-linear medium. The result: the beam remains focused for an unlimited time - as long as it continues to disperse in this medium. Amazing, isn't it?
Until 1996, all solitons, in every theoretical and experimental study in which they were studied, were seen as completely coherent entities; But my intuitions told me that maybe, if we use a non-linear medium that reacts slowly - much slower than the random fluctuations of the incoherent light - we could create solitons originating from the incoherent light. We began to perform experiments, and in 1996 we demonstrated a soliton composed of light with partial spatial coherence: laser light transmitted through a rotating light diffuser. A year later we presented solitons from "white light", which originate from the light of a simple incandescent bulb!
Those who led these experiments are my students Matt Mitchell (Matt Mitchell) currently a senior researcher at Infinera - a company engaged in the development of smart optical communication; Ming-feng Shih, currently a professor of physics at the National Taiwan University; And my postdoctoral fellow Zhigang Chen, now a professor of physics at the University of San Francisco.
In the first two years of the research, we had no theory - everything was based on intuition only. At the end of 1997 we developed the first theories, in collaboration with a very good friend of mine named Demetri Christodoulides, currently a professor at the University of Florida. The discovery of the incoherent solitons ("random solitons") revolutionized research in the field. Since then, such solitons have been discovered in many systems, among others in periodic structures and photonic crystals - research by Hrvoje Buljan, now a professor at the University of Zagreb, Oren Cohen and Guy Bartel when they were my students, and by Jason Fleischer when he was my postdoctoral fellow. Oren and Guy are currently faculty members at the Technion, in the faculties of physics and electrical engineering, and Jason is a professor at Princeton University in the USA. Non-coherent solitons were also discovered in non-local nonlinear media - work by Gaetano Assanto and Claudio Conti from Italy, and by Oren Cohen and Carmel Rothschild, who is currently a faculty member in the Faculty of Mechanical Engineering at the Technion . Many other researchers around the world are currently working on ideas based on incoherent solitons.
An interesting fact is that incoherent solitons have also been discovered in the time domain: pulses that do not expand in optical fibers. This important research was carried out by Antonio Picozzi from France. In recent years, incoherent solitons have also been discovered in non-optical physical systems. In 2006, incoherent solitons composed of spin waves in magnetic layers were observed [Mingzhong Wu and Carl Patton in Colorado]. Several years ago I showed, theoretically, together with Hrvoje Buljan, when he was my postdoctoral student, and Ami Vardi (a professor at Ben Gurion University), that incoherent solitons should also be found in matter waves.
The idea of ​​"random nonlinear waves" is now taking diverse and interesting directions, such as creating spontaneous patterns with weakly correlated waves, as I showed with my student Marin Soljacic (now a professor of physics at MIT), my postdoctoral fellow Detlef Kip (now Professor at the University of Hamburg, Germany), and Dimitri Christodoulides. I believe that in the coming years we will see new discoveries in the field of random nonlinear waves resulting from the interplay between incoherence, dispersion and nonlinearity.

What did you focus on in the opening lecture at the conference in Baltimore?
I talked about a phenomenon called "Anderson localization" of light: how a beam of light propagates in a medium characterized by random and different refractive indices, and when the light becomes localized thanks to that disorder. The idea of ​​propagation and location of waves in a disordered medium was proposed in 1958, when Philip Anderson studied the movement of electrons in a crystal containing disorder.
Anderson won the Nobel Prize for this research in 1977, but many fundamental questions remain unresolved to this day. This field of research entered the world of optics in the mid-XNUMXs by Sajib John and Philip Anderson, who realized that electromagnetic waves are a fertile ground for the study of this universal phenomenon, since by means of light it is possible to isolate the various effects that influence the development of "wave packets" ( wavepackets).
Equally important is the fact that through the light you can actually see how the propagation of the wave changes and/or position. Over the years, many research groups have worked in this field.
Describe your research on the Anderson location - what did you discover and what are you still working on today?
Several years ago we were able to show experimentally the Anderson localization phenomenon in a photonic crystal containing disorder. The importance of this study stems in part from the fact that it is the first experiment to demonstrate the Anderson position in any periodic system that includes disorder. In the following experiments we investigated the influence of nonlinearity on the location effects. This research, which I conducted with my students at the time - Tal Schwartz and Guy Bartel - and with my colleague Shmuel Fishman, led to many follow-up studies all over the world. The idea of ​​placing waves within a system that includes both disorder and nonlinearity raises fundamental questions, which have led to many debates. For example, the question of whether over time the wavepacket will eventually expand, or if the disorder will slow down the dispersion, as happens in a linear medium. The answer to this question is widely disputed in the scientific community. Our 2007 study was the first ever experimental study of location effects in a nonlinear system involving disorder.
In the last two years, I worked with my student, Liad Levy, and my postdoctoral fellow, Michael Rechtsman, on positioning in quasi-periodic crystals - for example, a Baal crystal with pentagonal symmetry.
Quasi-periodic crystals are in themselves a unique phenomenon in nature, and they were discovered by Professor Danny Shechtman from the Technion and explained by my colleagues Professor Dov Levin from the Technion and Professor Paul Steinhardt from Princeton; We all hope that the three will win a Nobel Prize for their discovery.
Liyad, Michael and I examined the propagation of waves in quasi-periodic photonic crystals, and to our great surprise we discovered that under certain circumstances the wave packet can go through a process called
disorder-enhanced transport. In other words, introducing disorder into a quasi-periodic crystal causes the light beam to expand more than it would in pure quasi-periodic crystals. Moreover, this expansion, which is counterintuitive - because disorder actually tends to reduce the expansion of wave beams - is characterized in a way reminiscent of diffusion processes: the average light beam has a Gaussian shape. The first article about this phenomenon recently appeared in the prestigious journal Science.
Finally, in the last few months we discovered another surprise: if the random disorder changes rapidly during the expansion, the light beam expands much faster than it would even in a perfectly homogeneous medium, with no disorder at all. At the same time, my postdoctoral students Alex Szameit and Michael Rechtsman studied amorphous photonic systems. These are disordered systems that have no Bragg diffraction at all, meaning they lack the most basic property of crystals. Despite this, we were able to prove experimentally and theoretically the existence of a "forbidden gap" - angles where light cannot propagate at all. The first article on the subject appeared this week in the journal Physical Review Letters.
I believe this is only the tip of the iceberg. The physics of optical systems characterized by disorder, linear and non-linear, is in its infancy. I expect many surprises in the coming years.
What discoveries can the optics community expect from your research group at the Technion?
We are working on several projects at the same time, probably because I have always liked entering new fields and learning new topics. But if I am asked to point to one discovery, I would say:
sparsity-based sub-wavelength imaging. This is work that I started two years ago with Professor Yonina Elder, an expert in the field of information processing, and my young colleague Oren Cohen, who added some excellent ideas on the subject
sparsity-based super-resolution in time and frequency spaces. Fortunately, we were blessed with some excellent students in this research: Yoav Shechtman, Shanir Gazit and Pavel Sidorenko, and Alex Szameit, an excellent postdoctoral student from Germany, who recently became a faculty member at JENA University.
What does the future hold in the field of non-linear optics?
Non-linear optics is a very broad field, and its potential research spectrum is enormous - among other things in the field of opto-fluidics, that is, light-fluid relations (see bottom frame on p. 16). Another research target is related to non-linear phenomena in metamaterials: artificial materials with electromagnetic properties that are engineered on a scale smaller than the wavelength. Ideas of this kind have already been proposed in many theoretical papers, but the experiments are few. There is no doubt that experiments in this field will lead to exciting ideas that have not been raised by theorists.

What is the best part of a physicist's life?
Discovering a new, unexpected or counterintuitive phenomenon. These are the moments that drive me.
Article: Angela Stark, Director of Communications at the Optical Society of America (OSA).
The interview was published in the association's journal, OPTICS AND PHOTONICS NEWS.

Looking forward to many surprises in the coming years. Professor Segev in the lab

Light and liquid: interrelationships
One of the future research goals in the field of non-linear optics is the combination of non-linear phenomena and opto-fluidics: combined dynamics of light and fluid. So far the field has been dominated by engineers and material scientists. "They did an excellent engineering job, but I have no doubt that the field is still not exhausted. It has been known for many years that light exerts forces on small particles that move when they are immersed in a liquid. The studies that were done focused almost entirely on the particles themselves, but there is no doubt that the particles moving in the liquid create movement in the liquid itself: they have friction, which creates a flow in the liquid that originates from light. At the same time, the light changes the local concentration of the particles in the liquid, and as a result the refractive indices of the "suspension" change - therefore the shape of the light beam also changes. There are three non-linear processes here that work in an integrated manner: light creates a flow in the liquid; The flow affects the concentration of particles everywhere in the liquid; And changing the concentration changes the refractive index of light everywhere in the liquid. As a result, the propagation of light in the liquid changes, and God forbid. This direction may lead to new basic physics, as well as interesting applications, for example control of drug dispersion using light, optical control of chemical processes (such as catalysis) with a precision of tens of microns, and more. This project was launched through a former student of mine, Carmel Rothschild, upon completion of his PhD (Carmel did a post-doc at MIT in the field of solar energy; he is joining the Technion Mechanical Engineering faculty this summer as a new faculty member). The project continued and reached great achievements through my other students, Elad Greenfeld, and Yuval Lemhot, and now Kobi Lomer (new doctoral student) and Dr. Yoni Namirovsky (Sabbathologist from Raphael.) have joined the project.

Don't let the fame fool you
Professor Segev, who has "raised" many graduate students, as well as many post-doctoral students, believes in the importance of the personal relationship between supervisor and student. "Don't let the fame fool you," he suggests to students and postdoctoral fellows who are about to choose a supervisor. "You want direct contact with senior researchers on a daily basis, not through a 'chain of command'. Before you choose a research group and a supervisor, talk to the students who are currently active in the group as well as those who were active in it in the past. They taught who the researcher is as a scientist and as a person. This is the man who will be your scientific father, or your scientific mother, so make sure you made the right choice. I was lucky enough to learn from one of the great mentors of the world of optics: my scientific father, Amnon Yariv from the California Institute of Technology. Amnon had a huge impact on my career.”
He also has advice for the young faculty members: to recruit students wisely and carefully, and not to rely only on high grades from the first degree. "It is impossible to draw any conclusion related to creativity from such scores. Let the new students work on small projects for two to three months, working closely with you. Consult with the old students and postdocs, then recruit only students who can think creatively. You don't want skilled people who excel at solving homework but are mentally fixed!"

Published in the Technion magazine

12 תגובות

  1. Creativity begins in education, especially in the early years. Education using the 'apsar' method brings people to the place where the educator wants them to go.
    The story about the elephant illustrates this well:
    In the arena of the circus, an elephant handler is seen leading a huge elephant with a thin rope at its foot. One of the children who was watching the elephant, asked his father. Father, why doesn't the elephant tear the thin rope that is attached to its legs, because the elephant looks so strong that tearing the rope does not require any effort from it.
    Listen carefully: said the father to his son. An act that was so was. When the elephant was brought to the circus many years ago, it was so small it could barely stand on its feet. That same day they tied the same rope to his leg. Immediately the elephant tried to free his leg from the rope, tried with all his strength, but as a baby elephant he had little strength, even less strength than you have now my son. He kept trying day after day for a long time.
    And what happened next? asked the son.
    The little elephant tried and tried and could not break the rope. And today he no longer believes that he is able to tear it.

  2. to an anonymous user,
    The phenomenon that Prof. Segev is talking about is the creation of a soliton, that is, a wave packet that does not expand in time. In the example he gives, the soliton is composed of incoherent light (white light from an incandescent lamp), something that is considered impossible, but as the article tells, it was done by Prof. Segev and his students. The wave packet that does not expand in time is the light beam that focuses the role of time in this example the direction in which the light progresses, which we will call the z direction There is a mathematical transformation that links the z direction to time in a three-dimensional problem. So in practice you get
    Creating a two-dimensional soliton in x and y directions that does not change its shape in time (z direction).

  3. A. Ben Ner,

    There is absolutely no shame in being uncreative.
    And I didn't understand how the example you gave is related to creativity that is relevant to our case.

  4. Gentlemen "the idealists of creativity".
    In general - you are wrong (except maybe a few exceptional examples).
    Creativity is a necessary condition for being a scientist and researcher but absolutely... not enough.
    The really important conditions are:
    * Perseverance, desire and diligence.
    * Suitable intellectual capacity.
    * Above average financial ability that allows you to focus and concentrate on your studies.
    * And the main thing..the main thing..the main thing, luck. Yes, yes... luck. And hopefully good luck.

    **Creativity is only in retrospect. If it succeeds... you can brag about the title of creativity,
    If it fails... it's a travesty.
    I have yet to hear that something brags about itself or praises the other person in praise of super creativity
    A failed idea. The irony of fate is that sometimes an idea fails at first and then it wins
    scorn and ridicule. Only after a period, if the idea is accepted, then it becomes "creative".

    I have already seen many times that people use the term "creativity" as a cover for failure
    And even to stupidity. and why? Because creativity cannot be measured.
    "I'm weak in mathematics, physics, and chemistry, but I'm creative, what is it?"
    Yesterday I bought clothes, what is beautiful and suitable? And blessed is the fat, perhaps good
    in studies..? But what shape does he have and what clothes does he wear" etc..etc..

  5. Segev is right:
    "Recruit only students who are able to think creatively. You don't want skilled people who excel at solving homework but are mentally fixed!"
    In practice (!!) many of the creatives are simply out there and often recruit the mentally fixed, because the creatives threaten the researchers in the department. And then the latter do not want the creatives to enter the department and they do everything to remove them. Therefore Segev's advice is empty of content and no one implements it.

  6. Eyal:
    I was aware of the difference when I wrote but I thought it was worth introducing the idea.

  7. I didn't understand the example he gave: "Imagine a simple light bulb, we focus part of its light into a beam 10 microns wide (a beam 10 times thinner than a hair), and direct it into a non-linear medium. The result: the beam remains focused for an unlimited time - as long as it continues to disperse in this medium. Amazing, isn't it?”
    Can anyone translate?

  8. Michael,

    Your claim didn't just win. You stood in front of someone who gives marks and constructs the exercises, and this is indeed a convincing claim. On the other hand, when it comes to our unsupervised academy, you have no one to make such a beautiful and just claim but to the nearest wall in your environment. It is possible that homework and exams in the first degree, some of them will be well structured and examine the person being tested in depth, but it is also possible that they will not. Most likely not. It depends on many parameters and even varies from university to university within the country.

    In my humble opinion, one of the roots of the problem in question is the unwillingness of the lecturers to be lecturers from the beginning. When a researcher is forced to pass a certain course, he has no teaching motivation, as far as he is concerned, all the dealing with the course is a waste of time and does not contribute to him, but only cuts him off from the time he devotes to his research. It seems that many of the lecturers are in such a situation. The consequences of this for undergraduate students are far-reaching. Without referring to the grades at the moment, one of the essential consequences in my opinion is a lack of motivation that is transmitted to the students themselves - only when a few and special of their kind will learn the course content properly and acquire the knowledge they are supposed to acquire despite the difficulties that the lecturer unintentionally raises. All the rest, even wise ones, left the course without the knowledge and tools they could have left with and deserved (and of course they were supposed to). Usually in these cases, knowledge accumulated in preparation for the test will spill over, achieve a satisfactory if not high score, and then go to waste. In this way, knowledge is not established and tools are not internalized. If it is about engineering, the result is a whole cycle of mediocre engineers who lack enthusiasm and desire to pursue a master's degree. (And all kinds of other results that can be deduced).

  9. The last sentence can be interpreted in several ways and it seems to me that the writer also did not draw the full conclusions from his experience.
    I will allow myself to tell here a short anecdote from the time of my military service, partly because of the dirt that Audi tried to pour on the army.
    I have an impressive record of 100 percent success in rescuing those of my subordinates who were candidates for impeachment in BHD 1 from impeachment.
    When a cadet goes before the impeachment committee, his commanders are allowed to appear before the committee and teach him a right.
    Generally, the commanders are not supposed to refer to what happened in the officers' course itself and they are supposed to limit their arguments to sentences that refer to the intended placement of the cadet, such as, for example, "We are dealing with a technological unit and his physical fitness is much less important than in other places."
    In one of the cases I completely deviated from this rule.
    The cadet's commanders in the course claimed that nothing interested him except the grades.
    My defense of him was based on the following claim:
    The grades are your way of making it clear to the trainee that you are satisfied with his performance.
    If he does something incorrectly - it should be reflected in his grades.
    If it is not expressed in grades - how do you expect him to improve anything?
    What is wrong here is the way you determine the grades and not the performance of the cadet.

    To the astonishment and heartbreak of the commanders in the course, Mofaz, who was the commander of the BHD at the time, accepted my argument and the cadet returned to the course and completed it successfully.
    In a framed article I will mention that he also returned to the unit and fulfilled his role as an officer in an excellent manner.

    The relevance here is clear:
    If the homework exercises you give also test creativity and mental instability, then you actually want skilled people who are excellent at solving homework exercises.
    It all depends on how you build the home exercises.

  10. To Eyal
    The problem is that the perception is based in the whole society.
    From jobs where the job description says "university graduates only"
    And university entrance screening only for those with psychometrics X or higher
    From screening tests before a position/purchasing an apartment in Moshav/and others who claim to know the complexity of the examinee in all its layers in 5 hours.
    In the army, IQ is determined by tests. (well maybe in the army it is necessary not to be creative)

    So how can you get out of this national fixation.

    a quote
    "Don't base yourself only on high grades from the first degree. "It is impossible to draw any conclusion related to creativity from such scores"

  11. The last sentence, so true! Please listen all of you and internalize.

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