Research Activities

The first quantum revolution was fueled over 60 years ago by the invention of the first laser, brought quantum mechanics into real-life applications and over time revolutionized many different areas of society. Nowadays, they are ubiquitous in our everyday lives, used in applications ranging from telecommunication, over medical treatments to barcode scanners.

In the past few years, the stage was set for the second quantum revolution, aiming for the manipulation of single quantum particles such as atoms, spins and photons. In the field of quantum computing, single atoms and spins are predestined stationary local qubits, while photons are the only possible flying qubit type for connecting distant quantum nodes. The award of the Physics Nobel Prize in 2022 for experiments using entangled photons will further spur progress in the realm of photonic quantum technologies, which promise applications in said quantum computation or secure quantum communication.

Our group is working on the development of such novel quantum devices, based on II-VI or III-V semiconductor nanostructures. For this, our research is based on three cornerstones, starting from material growth and development, over nano-processing of devices, to the optical and electrical characterization of prototypes. With this approach, our group covers the full value-added chain of research, technology and engineering.

The first major pillar of our work is material growth and development of compound semiconductor systems. This is performed within the Nanocluster , a unique multi-material cluster tool, which has several deposition systems for different material classes, all interconnected under ultra-high vacuum conditions. Typical materials are II-V compound semiconductors such as zinc (magnesium) selenide or cadmium selenide (Zn(Mg)Se, CdSe), which are especially interesting for future quantum emitters in the visible spectrum due to their excellent optical properties. Another prominent semiconductor system is the one of III-V semiconductors, such as gallium arsenide or indium arsenide (GaAs, InAs), which traditionally have been used for high-frequency electronics and optical applications in the infrared spectral range.

The cluster allows not only the epitaxy, i.e. the well-defined single crystalline growth of thin films on top of given substrates, but also the full in-situ combination of different material systems.

One example of current research in our group involves hybrid semiconductor nanowires. These quasi-one-dimensional structures, having a length of several micrometers and diameters in the range of several tens of nanometers, consist of a III/V material core and a surrounding II/VI semiconductor shell (see Fig.1). Those structures have a multitude of applications such as chemical sensors, lasers, photovoltaics or for future miniaturized electronics.

The second important cornerstone of our work is the fabrication of nano-scaled devices for different branches of quantum information technology. The starting point for this are our self-developed semiconductor heterostructures, which are processed to functional devices in the Helmholtz Nano Facility clean room.

Our group is working on flying qubit devices, i.e. on-demand sources of single photons, tailored from different resonators such as nano pillars or photonic crystals (see Figure 2a). In parallel, we develop optically and electrically controllable spin-qubit devices for future quantum computing . Furthermore, we are interested in transport properties of novel core/shell nanowire structures (see Figure 2b), which are an important building block for Andreev qubits.

The third and final cornerstone of our work involves optical characterization of the fabricated devices. For this purpose, we have a high-level and multifunctional quantum optics setup available, which allows us to configure a small lab-scale quantum network. This includes two closed-cycle cryostats with nano-positioning units, several pulsed and tunable laser sources, a photon correlator and an entanglement generator. It also includes a micro-photoluminescence setup for the characterization of single quantum devices, as shown in the left part of Figure 3. One possible structure, we’re interested in, are nano pillars made from II-VI quantum well heterostructures. These nano pillars , shown on the right part of Figure 3, are promising highly efficient emitters of single photons as we could verify in our photon correlation setup.