4 December 2020

Frank Deppe

Dr. Frank Deppe - Walther-Meissner-Institute & TU Munich

1. What is your current research focus? What is your role in the MCQST?

As a full-time scientist at the Walther-Meissner-Institute and as a lecturer at the Technical University of Munich, I am a so-called PI (principal scientist) in the area of quantum computing at MCQST. My research focus is on superconducting quantum circuits, i.e., superconducting circuits on silicon chips. These can be used to realize quantum bits, quantum memories, quantum limited amplifiers, quantum light sources in the microwave range, or sensitive detectors. In order to prevent the loss of important quantum resources such as superpositions and entanglement within a very short time, a high level of equipment and continuous optimization of the manufacturing process are necessary. From a scientific point of view, these circuits represent artificial atoms, which are particularly suitable for the investigation of light-matter interaction in the area of strong coupling. In the past, my group has done important pioneering work in the field of ultra-strong coupling. In addition, we belong to the leading groups in the field of quantum communication and quantum sensing technology with microwaves. I also coordinate the Quantum Flagship project Quantum Microwaves for Communication and Sensing (QMiCS). In this project, we pursue promising ideas such as local networks for quantum computer (quantum LAN), quantum communication with microwaves, or quantum radar.

Frank Deppe standing at his desk in his office at WMI. © F. Deppe

2. How does a typical working day looks like for you?

Meanwhile, I am only occasionally in the lab myself. Usually, I come to the office, switch on my computer and spend the day with paperwork and meetings. What I do is perhaps best described by the term science administration. This includes, of course, the supervision of students, PhD students, and young postdocs. They have the privilege of doing the actual laboratory work. Moreover, it includes the correction of publication drafts, Bachelor’s, Master’s, and PhD theses, which is also time-consuming. Other important activities are writing applications for third-party funding and, if successful, managing the scientific aspects of the resulting projects. On the one hand, the latter naturally includes very subject-related discussions on the progress of the project with the other group members and partners. On the other hand, I regularly report on the project results in various formats to the funding agencies, the scientific community, and the general public. Although this may sound a bit dry now, it does contain a considerable amount of creative possibilities, which one can only find in science in my opinion. Typically, the question 'How well does it work?' is not the focus of our projects, but rather the question 'Does it work at all?'. For this reason, I decided to pursue a scientific career in the first place. As a lecturer, I also have the obligation to teach. Passing on knowledge to students is a lot of fun for me, but during the semester, it also ties up a large part of my strength.

3. What was the biggest challenge for you this year?

This was and is certainly the change in communication due to the Corona situation. Especially the scientific exchange suffers from this, which simply works less well at online conferences. Normally, at a conference, you learn important details that are not found in the official publications and lectures over lunch, dinner, or a beer with colleagues. I am of course aware that I am complaining on a high level compared to closed laboratories, short-time work, or job loss. Nevertheless, I think that Corona has clearly had a negative influence on the scientific exchange.

4. Tell us a bit about your research and how you are connected in MCQST.

For superconducting circuits, the phenomenon of quantum coherence, i.e., the existence of superposition states, was first experimentally demonstrated in Japan in 1999. Since then, manufacturing and control technology has improved dramatically. As a result, superconducting circuits are among the world's most promising platforms in quantum computing. In this field, the development of scalable platforms with a large number of qubits is now dominated by industry. There, departments with approximately 100 employees are already developing and operating chips with up to 50 highly coherent transmon-qubits in a configuration in which closest neighbors are coupled together. It is even possible to buy computing time on some of these devices, although they are not yet of any practical use due to their size and lack of fault tolerance. In my opinion, it cannot be the task of academic research to compete directly with such structures. As a scientist, I am more interested in innovative concepts. In my case, these are quantum memories, novel qubit couplers and alternative architectures. In addition, we are working very intensively on the equally future-oriented topics of quantum communication and quantum sensing technology with microwaves. We were pioneers in this field 10 years ago, and today we are one of the world's leading groups. We have recently implemented a first communication protocol, namely the preparation of a quantum state at a remote location by means of previously distributed entanglement. In addition, we are currently setting up a 6m-long connection at millikelvin temperatures between two cooling devices together with our partner Oxford Instruments. These cooling devices are necessary for all superconducting quantum processors anyway. Microwaves are the natural frequency scale of superconducting circuits. Using them for communication eliminates a major barrier on the way to superconducting quantum LANs: the considerable conversion losses to the optical frequencies previously used in quantum communication, even after many years of intensive research. In the field of quantum sensing, we are working on experimental concepts for a quantum advantage in radar. All these ideas are currently still located in the basic research area that is particularly important for MCQST, but may well become relevant for applications in a few years.

Our work on quantum communication with microwaves opens up the possibility to think about the development of quantum LANs or even quantum supercomputers from many standardized superconducting quantum computers on medium and long-term time scales.

5. How does your research contribute to building a quantum computer in Munich?

The quantum computer is certainly the quantum technology application in which the potential benefits are most obvious, even for nonprofessionals. However, this field is already very much dominated by industrial development. This trend is likely to intensify in the future. The short-term contribution of my research is mainly to establish Munich as an attractive location for the underlying superconducting circuits. The development of future-oriented, innovative concepts in academia will then ensure that relevant companies or suitable startups build a quantum computer here. For example, the CEO of IQM from Finland, which now also has a branch office in Munich, learned his laboratory skills during his doctorate in my group. In parallel, we will certainly continue to develop smaller quantum processors in research projects. Of course, as I said, with a focus on innovation rather than scaling. Finally, our work on quantum communication with microwaves opens up the possibility to think about the development of quantum LANs or even quantum supercomputers from many standardized superconducting quantum computers on medium and long-term time scales.

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