Dear Dr. Wicht, thank you very much for the interview and your time. Can you introduce the Ferdinand-Braun-Institut and your own field of work to our readers?

The Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH), is an application-oriented research institute in the fields of high-frequency electronics, photonics and quantum physics. We research and realize electronic and optical components, modules and systems based on compound semiconductors. Our developments are key components for applications in the areas of communication, energy, health and mobility required by society. In our R&D activities, we cooperate closely with partners from industry and the scientific community - always with the aim of rapidly transferring research results into applications.

I myself head the Quantum Photonic Components Joint Lab and coordinate the Integrated Quantum Technology research area. In this research field, we work on topics that are aimed at applications in quantum sensor technology, quantum computing, quantum communication and quantum network technology. These research activities take place within the framework of four joint labs, which we operate in close cooperation with Humboldt-University in Berlin. The Ferdinand-Braun-Institut utilizes its many years of expertise in III/V semiconductor technology and optoelectronics as well as its globally unique hybrid microintegration technology. We also have an excellent technological infrastructure with clean rooms and laboratories with highly specialized equipment.

What core competencies does the general research area of integrated quantum technology encompass?

In quantum sensor technology, we cover the entire competence chain, from system design to the development of special components. Our focus is on the miniaturization of technical solutions at component level (physics packages, laser modules, light control units), at system level (e.g., compact optical atomic clocks) and on demonstrating the performance and reliability of technical solutions. This applies in particular to use in space. The optoelectronic concepts, technologies and solutions developed for quantum sensor technology, such as compact and robust narrow-band lasers, are also used in quantum computing with cold atoms or ions. Important core competencies are the design and semiconductor manufacturing of optoelectronic components, especially laser diodes and modulators. In addition, there is the hybrid microintegration of photonic modules (lasers, light control units), the UHV-compatible hybrid microintegration of optics in miniaturized physics packages and special product assurance measures for research into and implementation of hardware for use in space.

We also develop and manufacture single photon sources that use defect centers in various materials, as well as other functional elements required for quantum communication. Our core competencies here are photonic design as well as special semiconductor technology processes adapted to the material systems used (diamond, SiC). In cooperation with our joint lab partner at the HU Berlin, we are characterizing the performance of these components.

Which specific application areas are currently being researched at the Ferdinand-Braun-Institut and which methods are used in this work?

This is very extensive. I would like to give you an overview of the three areas of application that we are focusing on:

• In quantum sensor technology, our developments are aimed at
  • compact optical atomic clocks, atomic ensembles at room temperature, on the atomic beam or in the optical lattice for use in navigation, the synchronization of networks or the observation of climate change
  • Defect-center and gas-cell-based magnetometers, e.g., for use in medical technology or materials research
  • compact single-photon light sources for hyperspectral imaging in the mid-infrared and quantum optical coherence tomography
  • quantum enhanced imaging for the near-infrared wavelength range
• For quantum communication, we develop
  • Semiconductor components and modules for the generation of entangled photons using spontaneous parametric down conversion (SPDC)
  • Semiconductor components for single photon generation using diamond- or silicon carbide-based defect centers
  • We are also researching concepts for quantum amplifiers and their technical implementation.
• For atom- and ion-based quantum computing, we develop compact diode laser modules as well as compact and robust light control units (LCU) to generate coherent light pulses and to control them.

Are there any differences to conventional research approaches and processes?

Semiconductor technology allows us to produce very compact technical solutions. What's more, production using these processes is scalable, meaning that large quantities can be produced. A unique selling point is the hybrid microintegration technology that we have developed at our institute. It is unique in the world in terms of the complexity and performance demonstrated.

How can the research results achieved be transferred to integrable solutions in the future?

We are pursuing different approaches to integration. First of all, we implement the greatest possible technical functionality that is possible within a material system. Where this is not feasible, we use heterointegration processes at wafer level, which we develop for photonic solutions. Where this heterointegration is not or not yet possible or does not achieve the required performance, we resort to hybrid integration as an assembler technology. By optimally combining these methods, we achieve the desired functionalities and - if at all feasible - the desired performance.

What are the current challenges in basic and application-oriented research into integrated quantum technologies?

The degree of complexity of technical solutions is increasing, particularly in the context of miniaturization. In the ultra-precise hybrid microintegration of complex photonic modules, we have to ensure that they retain the necessary mechanical stability, even if their complexity and size increase. At the same time, we are in the process of transforming this microintegration into a technology suitable for industrial use in order to be able to assemble our modules reliably and more quickly in higher quantities. We are also investigating how we can bond reliably and accurately within ultra-high vacuum environments. Additive processes also play an important role, which we want to use to further miniaturize technical solutions.

A further challenge is heterointegration at wafer level with questions to which we are looking for optimal answers. Which material systems are best suited for wafer-level integration of active and passive photonic functions? If material systems are specified: What are suitable processes for the production of photonic structures and their heterointegration? How can we minimize coupling losses at interfaces?

Could you tell us more about the Joint Labs in cooperation with the Humboldt University of Berlin? How did the collaboration come about?

HU Berlin approached us many years ago in search of compact and robust lasers for use in space. Diode laser technology offers the possibility of realizing very compact and robust modules for the entire wavelength range, from the very near infrared to the blue and UV spectral range. More than ten years ago, this technical connection led to us initially cooperating on projects in the field of quantum sensor technology for use in space. This was so successful that we have since expanded and consolidated this collaboration with four joint labs.

What milestones have already been achieved with these project groups?

Our R&D work has since enabled groundbreaking progress to be made, particularly in the field of space-based quantum sensor technology. For example, the proof-of-principle of a rubidium-based optical atomic clock on board a sounding rocket was successfully demonstrated, as was an iodine-based frequency reference. The same applies to a Bose-Einstein condensate, which was demonstrated for the first time in space using our laser modules. The first realization of a matter wave interferometer on board a sounding rocket would not have been possible without our laser modules.

Berlin is considered an important location for technology and innovation. To what extent does the location offer additional resources for the development and implementation of research projects?

Research and development at Adlershof and in Berlin as a whole benefit from the large number of university and non-university research institutions. They are often technically complementary and therefore complement each other well. Berlin Partner and local networks such as OptecBB make a significant contribution to networking and exchange. Funding programs from Investment Bank Berlin support this cooperation between local institutions and partners from industry. The Berlin Quantum Alliance further strengthens local cooperation, in particular by providing funding for R&D projects with industrial partners for quantum technologies. We have also noticed that the first QT start-ups have now been founded in the Berlin-Brandenburg region. There are a number of locally based companies from the photonics sector that are also benefiting from the emergence of a QT industry sector. In addition, there are supra-regional associations such as the Research Fab Microelectronics Germany - the office is based in Berlin - which promote further networking in the high-tech sector, with the FMD-QNC specifically for quantum technologies.

How could research work at universities and institutes be promoted and driven forward at national and international level in the future? Are there specific approaches that the Ferdinand Braun Institut would perhaps also welcome?

It is not always possible to find suitable local project partners for all requirements in an R&D project. We would therefore welcome it if local funding measures made it possible to involve partners from outside the region or even internationally.

For spin-offs, we need funding programs that are more accepting of risks than in the past. On the one hand, the risks are of a technical nature because we are operating in a high-tech field here, many aspects of which are not yet anchored in the industrial sector. On the other hand, these start-ups are operating in a market that is only just emerging. The funding measures must therefore take particular account of the fact that the start-ups' own funds are generally manageable and that the break-even point in the development of a product is reached later than in areas with industrial manufacturing processes and developed markets.