Quantum simulators can mimic solids, that is, they simulate materials, but under very precise and controllable conditions and reduced to the essentials. From an experimental point of view, the researchers at the Max Planck Institute of Quantum Optics (MPQ), whose experiments Tim already admired as an undergraduate, are leaders in the field. In their labs, they use lasers to cool and trap individual atoms and arrange them into regular structures. However, whereas in a real solid, the regular arrangement of atoms forms the crystal lattice, with each atom at a fixed lattice position and the electrons moving in between, in a quantum simulator the atoms mimic the electrons. For example, the atoms can hop between different lattice sites and thus imitate the electron movement, Tim explains. What is important to note, he continues, is that the distances are much larger and the time scales are much longer. So the atoms in the quantum simulator move much slower than the electrons in a real material. “You can look in and really take microscopic images, say snapshots, of what is going on in these quantum simulators which is something you definitively can’t do in a real material.”

Stripped down to the essentials

Tim’s fascination with his field of research is obvious: “The key advantage of quantum simulators comes down to the tunability of the systems.” Real materials are extremely complicated things, he continues. There are many different mechanisms going on in them that affect each other. Electrons interacting with each other, electrons interacting with the crystal lattice, perhaps impurities or temperature playing a big role – these are just a few of many points that could be listed. “It’s hard to identify individual mechanisms that may be responsible for a certain physical behavior of the material,” the doctoral student explains, “The idea with quantum simulation is to really strip this down and come up with a model which is kind of the simplest possible model that we think captures the interesting physics that we want to observe.” 

And this is precisely Tim's task. As a theorist, he is not in the lab himself, but at his department they research and develop these “minimal models”, as he calls them. Typically, most of his day-to-day work involves performing numerical simulations on these models. “It's definitely a two-way street,” he says. On the one hand, he uses the numerical tools to verify and benchmark the trapped-atom experiments. But more importantly, he uses them to explore new physics. If the results of his numerical simulations are promising and point to interesting phenomena, he tries to come up with proposals on how to implement his minimal model in the lab. A specification could be, for example, what geometry the crystal lattice should have, whether it should be triangular or square, for example. The elements to be used for the simulation could also be part of the proposal.

“I’m working at the intersection of theory and experiment”

In the labs, the various parameters can be precisely set and controlled, the theorist explains fascinated: “You can tune the different interactions, you can tune the lattice geometry, you can tune the temperature to some degree and so on.” But, of course, not everything a theorist might dream of can be implemented. Close coordination with the experimental physicists is essential, the doctoral student emphasizes: “First of all, you have to go to the experimentalists and ask them what they are able to do from the technical side.” The great thing about Munich is that you have this close collaboration, he adds. Tim's Ph.D. project is a prime example of this, as his second supervisor, Johannes Zeiher, works as an experimental physicist in the MPQ labs. “I'm working at the intersection of theory and experiment” – that's exactly what Tim likes about his work.

He first came into contact with his current field of research during a summer research project during his undergraduate studies. Tim liked the topic so much that he wrote his bachelor's and master's theses on the subject. Even back in Australia, the theorist recalls, he always read the articles by researchers in Munich, especially those from experimental groups like the one at MPQ. “There's so much great research coming out of Munich. I thought at the time, wouldn't it be great if I could collaborate some day with these guys running these extremely cool experiments.” And now he can.

However, Tim's path did not lead him directly to Munich. At the end of his bachelor's degree in physics at the University of Queensland in Brisbane, he first applied for Ph.D. positions in the USA. Since, as in Australia, the doctorate follows directly after the bachelor's degree and a master’s degree is less common there, this was "a more natural choice", says the physicist. “But I didn’t get in anywhere in the US.” However, this did not deter Tim from his desire to pursue a Ph.D. abroad. He began his Ph.D. in Brisbane so that, after some time, he could have his work recognized as a master's degree and thus apply for a Ph.D. position in Europe. “One of my main motivations was to travel overseas.” Applications were sent to Oxford, Hanover – and to Munich for the MQV doctoral fellowship. “I have to say that this was the one I was least expecting to get,” Tim recalls, “I never really believed that I had a chance.” So the joy was all the greater when he was accepted. “I was really excited. There’s not many places in the world better than Munich for quantum science, the community is great.”

From the beach to the mountains

What Tim also finds great – at least almost as much as having the ocean 20 minutes away – is the proximity to the mountains. “In Australia, I didn’t do so much hiking, or bush walking as we call it back home,” he says. Here in Munich, however, he has now started to hike more. On his vacation in September, he and a good friend are going to Slovenia. They want to climb the Triglav, the country's highest mountain: “I booked the huts last night.” Another mountain on the bucket list is the Watzmann in the Bavarian Alps. But Tim's bucket list also takes him back to Australia. His home town of Bundaberg is also known as the “Gateway to the Great Barrier Reef”. He has never been snorkeling there, admits the doctoral student. Since leaving Australia, he has realized how many things he still wants to do there. “Visiting the Great Barrier Reef is definitely something that I should have done already,” laughs the Australian, “I really live not so far away.”

What he can do in both Australia and Germany is play chess. “My brother and I learned chess from a pretty early age from my dad, who was quite a good chess player,” says Tim. From the beginning he took part in chess tournaments and later was part of the school and college team. He played against Australian champions and once came second in the Australian Junior Championship himself. This year, Tim played in a chess tournament for the first time in four years: “I went to Karlsruhe and played in the GRENKE Chess Open.” This tournament is considered to be the largest open chess tournament in Europe. At the moment he is looking for a chess club: “I really want to play for a club in Munich.”

The doctoral student believes that he will return to Australia at some point. But for now, he is enjoying his time in Germany. Even though it wasn't the original plan, Tim is now all the happier that he ended up in Munich: “If I had to go back, I wouldn't change a thing.”

Published 30 August 2024; Interview 9 July 2024