RESEARCH

Phase-change materials (PCMs) offer a huge contrast in their refractive index when switched between an amorphous and crystalline state, for example exhibited as the data storage medium in DVDs. Combined with integrated photonics these materials widley open the door for many applications in all-optical signal processing and computing. First prototypes of all-optical multilevel data storage, an abacus for arithmetic operations and non-volatile switches have been developed and realized in our group.
A highly vivid and interesing topic of current research are unconventional computing architectures as neural networks, for example used for pattern and speech recognition. In our group, we investigate all-optical neural networks based on the phase-change photonic platform.

Diamond provides attractive material properties for both optical applications and mechanical devices. Especially defects in diamond offer one of the most promising platforms for spin-photonic qubits. They offer a discrete energetic level structure within diamond’s bandgap accessible with photons while also featuring long coherence times due to the low nuclear spin noise in diamond. We use Faraday cage angled etching to create free-standing photonic nanobeam resonators from single crystal diamond substrate. These resonators enable coherent coupling of the defect to our diamond photonic circuitry via the Purcell effect. Since our resonators are made of diamond, defects can be created via focused ion beam (FIB) implantation in the centers of our resonators. This allows for the fabrication of large-scale quantum registers.

Quantum Key Distribution (QKD) is crucial for secure communications in the quantum computing era. As quantum computing advances threaten conventional encryption methods, QKD offers inherently secure communication, regardless of an eavesdropper's computing power. Our project develops a QKD system using integrated photonics, combining indium phosphide's high-performance active components with silicon nitride's low-loss passive waveguides. We employ wavelength division multiplexing and time-bin encoding to increase key rates and transmission range. Cutting-edge superconducting nanowire single-photon detectors ensure high detection efficiency, while advanced electronics—including state-of-the-art FPGA boards and sophisticated software—facilitate high-throughput post-processing. Our work encompasses system optimization and characterization, chip design and packaging, high-speed electronics design, protocol implementation, and security analysis. This project aims to push the boundaries of quantum communication and deliver a practical, secure QKD system for real-world applications.

Superconducting nanowires allow for realizing single photon detectors with high timing resolution and quantum efficiency. We demonstrate the first nanophotonic circuits that incorporate such devices on chip. By fabricating nanowire detectors directly on top of waveguides we achieve near perfect detection efficiency, high timing resolution and a miniature footprint all in the same device. The results are the first step towards fully scalable single photon circuits at telecoms wavelengths.

Superconducting nanowire single-photon detectors (SNSPDs) are essential in quantum communication, computing, and photonic circuits due to their high efficiency, low dark count rates, ultra-fast response times, and low timing jitter. This high performance relies heavily on the quality of superconducting thin films, which directly impact efficiency, timing precision, and maximum count rates. SNSPDs function by absorbing photons, which disrupts the superconducting state and generates measurable voltage pulses. Key film properties—including thickness, crystallinity, and uniformity—are critical for achieving efficient detection and rapid response. Balancing aspects such as timing jitter, detection efficiency, and count rate is essential to tailor performance for specific applications. Achieving reproducibility in fabrication and consistent performance is also crucial for SNSPDs to meet the demands of quantum optical technologies, such as quantum key distribution and optical quantum computing.