It all comes together

Interview with Menno Veldhorst

Menno Veldhorst is group leader at QuTech and roadmap leader of the QuTech Academy. His story on how he got here almost seems like a preconceived plan. However, the truth appears to be very different.

During his PhD track in Twente, Veldhorst focused on superconductivity in topological hybrids. A subject that involved relatively simple experiments but a lot of complicated theoretical work, which earned him the Overijssel PhD Award in 2013. After this success, he moved to Australia, where he worked in a completely different field at the University of New South Wales. Over there, he studied silicon, a material that has already been the subject of a great deal of research. This gave him the opportunity to carry out complex experiments. From there, the step to QuTech was a logical one, he says: “Here, I can combine the knowledge I gained in my PhD with executing advanced experiments to make further progress in the exciting field of quantum information.”

It’s not as if his career path had been planned from the start, Veldhorst explains. “As far as my career is concerned I am not a long-term planner. I’m just very curious, so if I succeed at something I am keen to know how far I can take it. At the same time I’m not easily satisfied. When I feel I have thoroughly understood something I seek something new: taking a step so that I broaden my horizon or taking a step sideways. I think that’s a better way of looking at my career: not just in terms of content, but also in the way that my role changes. As a postdoc I was mainly trying to get my head around new ideas, while in my current role I have to consider whether I can convey it to my group as well. These are completely different aspects in my work that I have to focus on now. It’s precisely these changes that draw me to my work enormously.” In addition to being group leader, Veldhorst is also roadmap leader at QuTech Academy: “The more aspects my work entails, the more focused I become.”

He doesn’t feel it’s necessary to map out a route towards an ideal situation. “I might have to be careful with the advice I give to students, for whom I think it’s very good to think about their career path. I just feel it’s also very good to be able to deviate from it. You have to dare to make uncertain choices. Often, if the preconditions are right, you can steer and define a position along the way. Do not get stuck on a question like ‘Is this the perfect place?’ No, make that place perfect for you.”

That persistence is also reflected in Veldhorst’s research. When he worked on silicon qubits in Australia, many people thought this would never be possible. The team succeeded though, and Physics World named their publication in Nature as one of the ten most important physics breakthroughs in 2015. He is still working on removing obstacles to be able to realise a practical quantum chip. “The road to a quantum computer is like a big puzzle and I love putting the right pieces together in order to solve the puzzle. Even better if people think it won’t work, this motivates us even more to proof them wrong. No is not an option for me.” says Veldhorst.

Artist impression of two entangled spin qubits. The group of Veldhorst showed two-qubit operations in germanium and silicon, and in silicon even at temperatures above one Kelvin. Credit: Luca Petit.

Scaling up the number of qubits, for example, remains a problem: it is not yet possible to have a large number of qubits work together. A logical approach is to use qubits that can be produced using the production methods of classic chips, such as superconductor or semiconductor qubits. However, this is not a straightforward solution, because researchers are currently often counteracting the undesirable influence of the qubits by operating them at ever lower temperatures, and these temperatures are difficult to achieve with the millions of qubits needed for a practical quantum computer. Veldhorst is also working on this: his group has published a study in Nature that shows that silicon qubits can also operate at temperatures above one Kelvin. “This temperature is of course still very low, but it is already high enough for integrating the qubits and other electronics on the same chip.” according to Veldhorst.

A short while before, his group published another study in Nature on the use of germanium instead of silicon in the production of semiconductor qubits. Germanium, the material that was used for the very first transistor in 1947, shows a physical effect called spin-orbit coupling. Other qubits need external elements to control them, such as magnets or electrical wires. This is another factor that complicates the scaling-up. “Germanium quantum dots got all the essentials: these structures are made with the same technique as the transistors that we currently use as a building block for the classical computer, and we can make billions of these on a chip. We imagine that with germanium, qubits can be scaled up in the same way.” explains Veldhorst.

“It all comes together in my research on germanium: many of the physics concepts that I worked with during my PhD are also applicable to that material. This allows me to link those two focus areas in my career: on the one hand we understand germanium very well and we can experiment a lot with it, but on the other hand there are also many new things to explore further. We can bring all the elements together in a very controlled way, which allows us to explore new methods. For example, we can research whether there are other, better methods to make qubits. It is a material that lends itself well for the discovery of new opportunities in quantum technology, which I find very exciting.”

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