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Interview: Dr. Daniel Jirovec

Hi Daniel, can you tell us what do you do at the moment? Where are you currently working?

After I finished my PhD here at the Institute of Science and Technology Austria (ISTA), I stayed as a PostDoc to support the next generation of PhD students and to help them build on my results. For example, I am currently training new students in the cleanroom and assisting them in their measurements. I’m passing my knowledge on to the next generation. 

What research topics are you currently working on?

During my PhD I started working on implementing qubits in germanium hole gases. We showed for the first time how a singlet-triplet qubit works in these structures. In germanium hole gases, the g-factor difference between two neighboring quantum dots can be very large. In fact, we found it to be 2000 times larger than any value found in electron-based structures. This allows us to operate our qubits at very small magnetic fields, below 1 mT. The g-factor is also electrically tunable. We're trying now to replicate our results and to scale up the device size from a single to multiple qubits. To stay on top of the complex tune-up procedures of multi-qubit devices, we’re experimenting with strategies assisted by artificial intelligence in collaboration with the group of Natalia Ares at the University of Oxford.

What do you view as the next big challenge in this research field?

I think scaling up is the biggest challenge in all qubit platforms. There are many results demonstrating outstanding performance of single qubits based on different platforms. But when you try to scale it up, you are faced with crosstalk, you have readout issues, you have all sorts of things that can go wrong. So there are many engineering challenges to tackle to keep the qubit performance high. 

What excites you the most about hole spin qubits?

What excites me is that there is still a lot of physics to explore in hole spin qubits. For example, spin-orbit interaction is a dominant effect for holes, but there is not much experimental work on it. We saw that in every device, the effects we observed were slightly different than those predicted by theory. In one experiment, we were exploring a spin-orbit term that was responsible for spin flips. We saw that the g-factors in one direction had the same sign and in another direction they had opposite signs. Our collaborators Philipp Mutter and Guido Burkard at the University of Konstanz developed a theory for this surprising result and we published it together in the Physical Review Letters.

To explore and unveil such hidden layers of physics is not at all straightforward, but definitely exciting. When measurements start deviating from the theory, that's when you know you’re on the trail of something interesting.

What is the next milestone coming up in this area of research?

Showing that you can operate larger arrays of qubits that interact with each other will be the next big step. Spin-photon coupling can play an important role in this journey of scaling up. This effect can enable connecting qubits over larger distances. It has been shown in silicon that spin-photon coupling can be much stronger for holes than for electrons. Finding this also in germanium, and using it to connect qubits in, let’s say, a 4-by-4 array, would give you a basic building block that you can scale up.

Can you tell us about the work environment at ISTA?

ISTA is a research institute close to Vienna. Various disciplines are represented on campus, which creates a multi-faceted work environment. On the practical side, we have a cleanroom with all the machines that we need available just downstairs from our offices. This gives me a lot of flexibility in planning how to address my day-to-day needs. I can often come in the morning and book three e-beam slots without a problem. 
The state of Lower Austria as well as private investors are strongly supporting ISTA. The resources and infrastructure on campus are outstanding and the individual research groups are well-funded. Technology startups find an excellent location and environment at our IST PARK. It's really a great work environment here for fundamental science. 

How did the HDAWG and UHFLI instruments support you in your work?

The UHFLI is probably the most used instrument in our lab. Almost every setup has one, because it's just so versatile and so quick to use. Starting to work with it was a bit overwhelming for me, it’s unusual to just have a box with no buttons to push. But the UHFLI comes with a very intuitive graphical user interface, which makes it very straightforward to become productive using it. 
Our qubit challenged the maximum performance limits of the HDAWG and of the UHFLI at times. But with the support from Zurich Instruments, we managed to overcome almost all the challenges. For instance, the LabOne update introducing the command table feature for the HDAWG was really helpful, it allowed me to use the instrument in exactly the way I wanted. There were struggles on the way, but I think this is normal for any scientific instrument: if you want to get everything out of it, you need to dig deep.

What is your next personal milestone?

I just accepted a new job at QuTech in Delft, so I will continue in academia for now. QuTech offers an excellent environment. It’s probably one of the most renowned addresses in Europe. There are many opportunities for researchers like us to stay in academia, or to take on a job in a startup. That is probably where I will end up: in an R&D department where I can do a little bit of this research and, you know, get excited when I see something weird.

What do you like to do in your free time?

I have a dog, which I often walk around the city. It’s a relaxing activity, but it’s also a creative one because it lets you think about whatever comes to your mind. I also play darts, this season in a league, which I do together with my father - that's our father-son activity. I also like cooking, enjoy good food and recently I started bouldering and climbing. 

Thank you for sharing your insights during this interview.

Dr. Daniel Jirovec

Dr. Daniel Jirovec, postdoctoral researcher at Institute of Science and Technology Austria (ISTA)

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