#QUSTEC Portrait: From Seaworm Genes to Magnetism in Microwave Fields

“The thing I like best about my work here is the free-minded spirit of my supervisors,” says Daria Sostina, who currently is a QUSTEC doctoral student at the Institute for Quantum Materials and Technologies (IQMT) of Karlsruhe Institute of Technology (KIT). “Working with Professor Wernsdorfer and Dr. Philip Willke is very different – everything here is much faster and more advanced than elsewhere. They do certain things in a short time, for which other people normally need years.” Daria especially appreciates the freedom she is given for her work at KIT and the fact that Professor Wernsdorfer and her supervisor Philip Willke are open to new ideas and possibilities. “I am not just a technician who is helping the bosses to scrub the vacuum chambers. I can actively participate and share my ideas,” she says. “I really value that.”

She arrived at KIT in March 2020, just when the Covid pandemic hit Germany. Nevertheless, she felt warmly welcome and her transition to her new position went smoothly. “It was very helpful that I already knew Philip from a former research stay in South Korea and was already familiar with his research field,” Daria says. Born in Russia, she had already been interested in natural science when she was in school – but she did not start with physics right away when she entered university in Russia. “At first, I was interested in biology and worked in the fields of embryology involving genetic research of seaworms.” But soon she realized that genetics wasn´t the topic she would like to spend the rest of her scientific career with. “It wasn´t long until I turned to physics”, she says. “The experiments are much more predictable and I like that better.” Daria started to work with magnetism during her bachelor’s studies and investigated topological insulators and graphene at the synchrotron light sources BESSY in Berlin and SLS at Paul Scherrer Institute in Switzerland. After another research stay in Korea, where Philip Willke was working as a postdoc, she was conferred her master’s degree at the Swiss Light Source SLS.

Her doctoral research at KIT is scheduled for three to four years. Her doctoral thesis deals with the design of new techniques for control and manipulation of magnetization dynamics of small magnetic devices with microwave fields. “What we mean by `small devices` is one single atom or one single magnetic molecule. The idea is to use Scanning Tunneling Microscopy (STM) to manipulate or move this single atom to a specific location and then to manipulate its magnetic state, also known as spin, by using radio frequency fields,” Daria explains.

In her research she is using a very small refrigerator developed by Professor Wolfgang Wernsdorfer, a pioneer in molecular qubits. This refrigerator is used for cooling to very low temperatures of less than 20 mK, very close to absolute zero. “We are able to play not only with electron spins of atoms and molecules, but also with nuclear spins that have a behavior more suitable for quantum computing,” Daria says. The experiments are carried out under vacuum in order to prevent atomic-scale contamination on the sample, such as water molecules. “A home-built superconducting vector magnet allows us to apply a magnetic field of few tesla in any direction. This is essential to play with spin qubits,” explains Professor Wernsdorfer.

Due to the Covid pandemic, getting to know co-workers and the city of Karlsruhe was difficult for Daria. Still, she has settled in well and feels comfortable in Karlsruhe. “Curiously, the city sometimes even reminds me of Russia,” she says. “It is not old and the architecture is relatively new.” Between the lockdowns, when restaurants were open, she found the opportunity to try out some German food as well. “I like ‘Käsespätzle’, a regional dish which is somehow a bit like a local version of mac and cheese.”

Asked for the most striking differences she experienced in her work in different countries, Daria answers: “Europe’s population is very spread – cities are very small compared to St. Petersburg or Seoul, where millions of people live. In South Korea, everything is very fast and very dynamic. They built a whole lab in less than a year, working 24 hours a day, every day. In Germany, I would say that the people have the tendency to look at the big picture rather than the details.”

What Daria likes about the QUSTEC program is that the doctoral students in Germany, France, and Switzerland are expected to exchange experiences. “I have worked in so many different countries and the international orientation of the program was an important aspect for me to apply.” Part of the program is a research stay in an Eucor country (for Daria, this would be Switzerland or France) for a period of six months. “I hope that the Covid situation will allow that soon. I would love to go to the IBM Research Lab in Zurich,” Daria says.

Her original application was for another QUSTEC project, but when Professor Wernsdorfer got hold of her documents, he became interested and asked her to join his project. “He told me he would have Philip in this project and spoke about his research idea. It wasn´t hard for me to decide that I would come,” Daria says. It is important to stay open for any possibilities, she continues. “My advice for other students is to take initiative, inform yourself, ask people about projects – that´s how I got to know about QUSTEC.” Philip Willke confirms: “We often have interesting projects and are looking for the right people to work with. It is surprisingly hard to find suitable doctoral students, especially international ones with such a wide experience as Daria. When people like Daria take initiative and contact us, we are more than happy.” Professor Wernsdorfer is convinced that programs like QUSTEC produce a win-win situation for both students and research institutes. He says: “The QUSTEC program is a great opportunity to attract excellent students from abroad, and Daria is one of my best students right now.”

For Daria the most important things are flexibility and commitment: “Know what you want, take your chances, stay flexible, and don´t take or stay with any position. I moved to Switzerland although my group in St. Petersburg was great, but I wanted to gather new experiences. When the position in Switzerland turned out to be not the best, I kept my eyes open for new opportunities and here I am now at KIT.”

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