Studies examine the Innovation Potential and Challenges of Light Sources and Single-Photon Detectors for QKD:
Powerful Quantum Computers could already be capable of breaking currently used encryption algorithms as early as the 2030s. This poses significant risks, particularly for the communication of sensitive data. Against this backdrop, Quantum Key Distribution (QKD), which promises physically secure communication based on quantum mechanical principles along the transmission path, offers a viable option for transmitting highly confidential information. For this reason, it is considered one of the key technologies identified as particularly worthy of support within the Hightech Agenda Deutschland adopted in July 2025. In this context, the Fraunhofer-Institut für System- und Innovationsforschung (ISI) published two new reports in early April 2026 that examine the innovation potential and key challenges of QKD use cases in detail.
In the roadmap “Light Sources for Quantum Key Distribution – Technology Overview and Future Perspectives,” the authors provide an overview of coherent laser sources for QKD with discrete and continuous variables, photon-pair generation via parametric fluorescence (Spontaneous Parametric Down-Conversion, SPDC) and Four-Wave Mixing (FWM), as well as Quantum Dot Sources and other deterministic emitters. According to the study, mature laser sources currently dominate QKD systems. However, photon-pair generation is advancing, especially for the field of entanglement-based QKD. Quantum Dots and other deterministic single-photon sources show promise for future advanced protocols and Quantum Networks. Nevertheless, further technological development is required, particularly regarding telecom compatibility and cost. For commercial adoption, robustness, high repetition rates, integration potential, and cost-effectiveness are also essential. In addition, component specification and certification, traceable metrology, standardized characterization, and system-level co-optimization with detectors play a crucial role.
The roadmap “Photon Detectors for Quantum Key Distribution – Technology Overview and Future Perspectives” focuses on silicon single-photon detector (SPD) technologies for DV-QKD, in particular silicon single-photon avalanche diodes (Si-SPADs), indium gallium arsenide/indium phosphide SPADs (InGaAs/InP-SPADs), and superconducting nanowire single-photon detectors (SNSPDs). The choice of detector depends on application scenario, distance, key rate, cost, and integration needs. The report assesses the suitability of these detectors across fiber, free-space, and satellite links, highlighting essential trade-offs between performance, operational overheads, and costs. The study shows that SNSPDs deliver unmatched performance, enabling the highest key rates and longest distances, but require cryogenic cooling. Si-SPADs are mature, cost-effective, and well suited for free-space and short-range links, but are not suitable for standard telecom wavelengths that are typically used in fiber-based communication. InGaAs/InP-SPADs provide a balanced trade-off between performance and deployability for fiber and free-space links at telecom wavelengths, but have comparatively low detection efficiencies and higher noise. Overall, detector choice for QKD should be guided by the specific application scenario – particularly distance and key rate – while also taking cost, cooling, and integration constraints into account. Further technological advances are anticipated in this area.
Source reference: https://www.linkedin.com/posts/fraunhoferisi_qkd-activity-7447176291285495808-zmA1?utm_source=share&utm_medium=member_desktop&rcm=ACoAADGNcwQBDlrUEOZSLZkJAAUZiCxLCTo51No