Superconducting metamaterial for analog quantum simulation – Vera Weibel studies an artificial material with special properties

Vera Weibel wrote her prizewinning master’s thesis at EPFL under Professor Pasquale Scarlino, having studied a superconducting metamaterial — an artificial material with properties that do not occur in nature. A material of this kind could potentially be used to prevent losses in quantum systems.

Vera Weibel will receive one of the two prizes for the best master’s thesis in nanoscience at the University of Basel in 2022. In this thesis, she investigated a superconducting metamaterial. (Image: C. Möller, SNI)

Researchers around the world are searching for artificial materials with optical, electronic or magnetic properties that do not occur in nature. These “metamaterials” consist of periodically arranged elements with a micro or nano structure. The size of these structures must be smaller than the wavelength of the phenomenon that is to be observed. Researchers typically begin by designing the materials on the computer and calculating their properties before producing and studying them in real life.

A material with a tiny, periodic structure
In her master’s thesis, Vera Weibel developed one such metamaterial with superconducting properties by periodically arranging the starting material, niobium nitride, into individual structural elements with a size of approximately 50 micrometers. These elements act as resonators — systems that vibrate in response to excitation in a specific frequency range. As a result of the chosen size of the structures, this chain of resonators vibrates in the microwave region and can therefore store microwave photons. The degree of coupling between the resonators and their respective neighbors can be fine-tuned by varying the distance between them — the closer they are to one another, the better their coupling, and vice versa. In the metamaterial studied by Vera, the resonators had alternating spacings. This meant that the photon states in the material could be described using a specific model (the Su-Schrieffer-Heeger model) that was originally developed for polyacetylene.

“In the future, it may be possible to use the material for analog quantum simulation — a branch of quantum computing,” Vera says when asked about the potential applications of a metamaterial of this kind. “The idea is to “reconstruct” the quantum system with components that obey the laws of quantum physics and that can simulate a specific quantum problem. The metamaterial I studied could be coupled to a qubit in order to study loss mechanisms in quantum systems,” she adds.

 

Design, simulation and analysis
Vera began by designing the structure on the computer and calculating its theoretical properties using simulations. The structure was then produced by colleagues from her working group at EPFL. In subsequent practical experiments at temperatures close to absolute zero, Vera was able to verify the reliability of the simulations. “We were pleasantly surprised at how well the simulations agreed with the actual results,” she says, summarizing this initial phase of her work.

In Vera’s case, the master’s thesis at EPFL came about thanks to a contact of her project supervisor, Jann Hinnerk Ungerer from the Schönenberger team at the Department of Physics. “The topic was very interesting and also gave me a chance to get to know another research institution outside of the University of Basel,” says Vera.

She had a great time in Lausanne, brushed up on her French and learned a great deal. At the same time, she experienced the advantages and disadvantages of working at a significantly larger institution. “For example, the clean room at EPFL was better than the one in Basel. On the other hand, the sheer size of the institution meant that I had significantly less contact with other research groups,” she says. The situation in Basel is quite different — especially among the nanoscience students! This small group of students are very well connected with one another and regularly exchange ideas.

“What particularly impressed me about this work was the amazing agreement between the theoretical prediction and the experiment.”

Professor Christian Schönenberger, Department of Physics, University of Basel

Vera first designed the superconducting metamaterial on the computer and used simulations to theoretically calculate its properties. (Image: C. Möller, SNI)

Not what she expected
When she started studying nanoscience, Vera didn’t imagine that she would one day complete her master’s thesis in experimental physics. After all, she first attended the bachelor’s information day at the University of Basel in 2015 because she was interested in studying biology.

“That was when I heard about the nanosciences degree for the first time, and I was sold on the idea immediately,” she recalls. “I thought it was great that the nanosciences degree began by giving us an insight into all of the natural sciences and that only later did we decide what we wanted to study in greater depth.”

After starting the degree, it took Vera a while to develop her passion for experimental physics. “In the block courses during the bachelor’s program, I primarily chose courses relating to biology and IT. Then, during the master’s program, I realized I was particularly interested in experimental physics and gradually began to focus on that area.”
That being said, she doesn’t regret having gained considerable experience in other subject areas, and she would begin her scientific career with a nanosciences degree in Basel again in a heartbeat. “The interdisciplinary nature of the program really taught me to think in a joined-up manner and to familiarize myself with new topics quickly,” she says.

The next milestone: a doctoral dissertation
Indeed, Vera is already familiarizing herself with another new topic. In March 2022, she began her doctoral dissertation in Professor Andrea Hofmann’s newly founded group at the Department of Physics of the University of Basel. She is studying specific quantum mechanical states in germanium-silicon heterostructures that she hopes to couple with a superconductor. In this work, Vera benefits not only from her knowledge of semiconductors that she gained from her master’s thesis, but above all from the organizational skills that she picked up during her studies and wide-ranging project work.

Vera is looking forward to the months and years ahead as she works on her dissertation, which has got off to a very positive start. “I’m in a great young team and have really enjoyed the work so far,” she says.

Further information:

Research groupPasquale Scarlino, EPFL
https://www.epfl.ch/labs/hqc/

Short video with Vera and Mathias
https://youtu.be/DyoPupfgaMs