research bits

by Liran Goldshtein


Even during these crazy days of economic uncertainty, a mysterious virus on a mission to conquer the globe, and a social protest that takes Israel by storm - Dr. Michael Krüger, Assistant Professor and Senior Lecturer at the Department of Physics at the Technion, doesn’t have time to sit and relax. He continues to work on his research.

“I am always fascinated by light, not just by the scientific aspect of it that has always been a secret”


Dr. Michael Krüger is a new faculty member at the Technion Physics Department. The interview with him is taking place in his new office at the Solid State Institute. “This building is from the 1970s”, explains Michael, “It’s well built, according to all standards, and is undergoing renovations”. The walls of the recently received office are still naked. Michael is currently sharing this workspace with one of the institute’s engineers. “We work in ‘capsules’ because of the Coronavirus, sometimes I am here and sometimes he is here”. The Coronavirus is looking for new victims, after all.

Michael does not define himself as an ‘Oleh Chadash’ or a typical Israeli immigrant - he does not have any Israeli roots nor a Jewish background. Despite this fact, he decided to move to Israel from Germany, after completing a Ph.D. at the Ludwig Maximilian University of Munich. “I am here because I like the country. I came here six years ago after my Ph.D. studies. I looked for a postdoc position, and I did not want to do what everyone else does, typically going to the United States or other English-speaking countries. I knew Israel a bit, I have friends here, and I knew the science and research are at a very high level. And so, I went to the Weizmann Institute for my postdoc, and met my wife in Rehovot. She is not a physicist, she is a musician, a piano teacher. She is an Olah Chadasha. We are now married for one year”.

He sees his move to Israel as an opportunity for a new life. “I started a completely new job with a lot of new responsibilities. As an assistant professor, I have to take care of a lot of things that I did not have to worry about before. For example, to instruct students, to give lectures - this is all new for me”.


Tell us about the differences between working in Israeli institutes versus German ones

“I feel quite well in the Israeli culture because I am also not a typical German. I come from Bavaria, which has a relatively warm weather. But some things are different. For example, the academic system - in Germany we have very strong structures, hierarchy, and authority. In Israel it is a flat hierarchy - you can talk to everyone. Also, the students are very independent, sometimes maybe too independent. They have their own ideas about everything. What I had to learn is the discussion culture - you cannot just rely on your experience, your title, or what you did before for people to accept what you say. You need to explain and justify everything to convince people. These discussions can be tedious, but sometimes something nice can come out of them, which I or the student did not think about before. In terms of original thinking Israel has an edge over Germany and other places, although “chutzpah” makes discussing sometimes a bit difficult”.


What advantages are there, in your opinion, in working at the Technion compared to other Israeli Institutes, also for students who are thinking about studying here?

“I think the Technion is a very strong institute because it is a real university. It has a very diverse student body and many departments that I have not been exposed to in my academic life since my university did not have engineering or technological studies. Maybe I had a bit of a negative view on engineering, but now, knowing many people from these departments, I think there are a lot of things that we can learn from each other. To have this interdisciplinary environment where you meet students from many different backgrounds gives you an opportunity to collaborate. This is a strong point of the Technion. Here on campus we have a cross-section of the Israeli society, and the Technion attracts a wide variety of students. It is amazing to see everyone in one campus, all with a common goal - to learn, study, and do research.

Another strong suit is the location - I think Haifa is an excellent location, it is one of the most pleasant places in Israel”.

Dr. Kruger at his temporary lab


How did you end up in the field of physics? Were you interested in the field as a child?

“I was not aiming to study physics. I had different ideas about life, but after finishing school I decided to go into physics because there was that dream to discover something that no one else has found before, to invent something that has not been there yet. This kind of drive was always there in my life”.


So why physics, of all fields? You can discover new things in almost every aspect of life

“It is also the question of what holds our world together - what are its laws and hidden realities. Particles, matter, light - I am always fascinated by light, not just by the scientific aspect of it that has always been a secret. It is hard to understand that light can be a particle and can also be a wave. We talk about this duality, but no one can describe what it actually is, we just lack the words for it. That is why we need to use two words to describe light -- particle and wave. These kinds of mysteries and puzzles intrigue me”.


Tell us about your research

“I want to look at a regime that is not very well explored. It is the regime of attosecond electron dynamics. This domain is the dynamics of electrons in matter, for example an atom, a molecule, a solid system, a crystal, or a nanostructure. We have electrons that are moving inside these materials, and these electrons interact with each other. They ‘talk’ to each other on crazy time scales, which is the attosecond time scale. One attosecond is a second divided by 10 to the power of 18. A nice comparison is taking the age of the universe, approximately 13.7 billion years, and relating it to one second. This is approximately the same ratio as taking one attosecond divided by a second. This is how fast electrons interact with each other and with light when they are exposed to it. Electrons are the lightest elementary particles, which are also charged with a negative charge. This means that they interact by electromagnetic waves, and they do so very fast”.

Michael works with the laser

Michael continues and explains that there are many open questions regarding these short periods - the attoseconds. “One of the questions we ask ourselves is ‘can we find new physics where electrons talk to each other in a way that has not been observed before?’ For example, if you take out an electron from a material and put it into some higher energetic state, you leave behind a hole. This hole is nothing other than all the electrons that are there, minus one electron. To create this “hole phenomenon”, all the remaining electrons interact with each other. It is physics that we have studied, but we do not know how fast the electrons rearrange to create the aforementioned hole. It is very hard to quantify this speed in an experiment, so theorists can calculate how these electrons rearrange themselves, but to observe and understand how this hole comes into being at the attosecond time scale - this we do not know yet. There is a lot of mystery surrounding this topic, and the goal of my research is to look at these effects in the time and space where they happen”.


What is the end goal of your research, except for trying to understand the hole?

“This is fundamental research designed to increase our knowledge regarding what happens on these short time scales of the attosecond. We create the aforementioned hole by light, using laser pulses, and we hope that by manipulating the properties of the light we can control what happens to the electrons. The technical term for this is ‘coherent control’ because the properties of the light waves are transferred to the electrons in the matter. This could lead to applications where we can control chemical reactions in molecules using laser light”.


Will your research have implementations in everyday life?

“This is a hard question to answer. This ‘coherent control’ is more in the name of science. I believe that possibly in the future we will be able to use light waves to control electric currents. For example, if you think about your computer or smartphone, it can perform about one billion operations per second with a clock rate of one gigahertz. If we could use electrical switches that operate by light waves we could possibly create a new level of electronics - the electric currents will be switched on and off by light waves on the attosecond time scale, or petahertz clock rate (which equals to a million gigahertz). There is a long way to go before we can put this into practice, if at all, but it is an interesting prospect of our work here.

For my research, I will build a new type of microscope. It is something that has not been attempted before. This microscope will have a spatial resolution that will allow it to image atoms, and simultaneously measure electrons in the attosecond time scale. It will be an ultra-fast scanning tunneling microscope, a one of a kind machine in the world. Today some microscopes can image electrons in time or in space, but not simultaneously. This will be the innovation of our microscope”.


Are there researches parallel to yours in the world?

“Yes, we are a part of a research field that goes into these questions. We are currently inclined to establish collaborations, but this is more about the applied side of the research rather than the research itself, which we lead”.

To help him establish the best starting point possible for his research, Michael received space for his new lab. The to-be state of the art lab is currently under construction. “The lab should be ready in half a year, and I am already working in a temporary lab. We started doing research there using lasers and with the help of students. In terms of funds, we are very well funded - the European Union has decided to award the ideas we would like to research with a grant. Aside from the generous support of the Technion and the Helen Diller Quantum Center, the Israeli Science Foundation has also agreed to fund these ideas, so I think I am in a very good position here at the Technion to realize all these ideas with my group”.


What qualities are you looking for in your research group?

“The most important thing is for people to be curious and open to go into something that has not been attempted before. Curious, intellectually courageous people! It does not matter if they worked in other fields before. What we do is unique and combines many different fields, which makes this research particularly interesting, challenging, and exciting. I do not have a specific target audience, but of course, it is all about experiments, so we need good hands for optics and nanoscience”

Dr. Kruger and his team- Amit and Abraham


We are ascending to the next floor and arriving at a large space that within approximately six months will become Michael’s new lab. The technicians and handymen are working behind the walls, drilling, and laying cables. The walls are still just bare concrete, and it only remains to be imagined how this big room will look like half a year from now. “Due to the sensitivity of the equipment we will need a very strong air conditioning system, and this is one of the reasons the assembling of the lab will take time”, explains Michael. “The building and the lab have existed since the 1970s, the machinery that was inside the lab was also from the same period, and this year we took everything out so we can renovate”.

The new lab is being built


Our next station is the lab Michael is currently sharing with Dr. Ido Kaminer. "Our laser is not really dangerous, but we need to make sure that it is secured", explains Michael before he signals that it is possible to step through the double door into the lab. “This is a small optics lab. We have this special table with holes inside and you can basically play Lego”. Michael shows the metal desk which is covered with screw holes and the little optical components you can move around to any of the holes across the table. “Here we have optics such as mirrors, lenses and other optical components, and the laser can run through them”. The scene looks very impressive like it was taken from a sci-fi movie. “At the moment we are characterizing the laser pulses, which are about six thousand attoseconds long, and they are good for shaping the waveform. By characterizing these pulses we can later try to build, for example, the aforementioned ultrafast microscope. We also design vacuum chambers for the microscope, and we hope that in a few months we will start doing experiments on matter”.

Optical components for experiments


Only after stepping out of the lab, one can truly realize how cold it was inside. The low temperature is vital to keep the electronics from heating up and to prevent long term damage. It seems Michael’s team does not have any objections to the cold inside. After all, it is the peak of the Israeli summer outside.