Paving the way for secure quantum communication networks
The emergence of quantum computers is making conventional encryption methods more and more vulnerable. To make communication secure, they need to be replaced with quantum key distribution (QKD), a technology that safeguards transmitted information against attacks by eavesdroppers. QKD makes use of the properties of quantum physics to secure data transmission, but the limitations of existing quantum light sources have made setting up large networks difficult. A team of German scientists supported in part by the EU-funded MiNet and Qurope projects and the European Metrology Programme for Innovation and Research have now conducted the first intercity QKD experiment with a deterministic single-photon source (SPS). Described in their study published in the journal ‘Light: Science & Applications’, this achievement will revolutionise the way our confidential information is protected from cyberthreats. “We work with quantum dots, which are tiny structures similar to atoms but tailored to our needs,” explains study senior author Prof. Fei Ding of MiNet project coordinator Leibniz Universität Hannover (LUH) in a ‘Newswise’ article. “For the first time, we used these ‘artificial atoms’ in a quantum communication experiment between two different cities. This setup, known as the ‘Niedersachsen Quantum Link,’ connects Hannover and Braunschweig via optical fibre.”
From Alice to Bob
The experiment took place in the German federal state of Niedersachsen, with a 79-km-long fibre connecting the LUH in Hannover and Germany’s national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), in Braunschweig. The transmitter Alice, located at the LUH, statically prepared single photons encrypted in polarisation. The receiver Bob, located at the PTB, contained a passive polarisation decoder to decrypt the polarisation states of the received single photons coming through the fibre-based quantum channels. “Quantum dot devices emit single photons, which we control and send to Braunschweig for measurement. This process is fundamental to quantum key distribution,” notes Prof. Ding. The result was a stable and rapid transmission of secret keys. The researchers first verified that positive secret key rates (SKRs) could be achieved for distances up to 144 km corresponding to 28.11 dB loss in the laboratory. The deployed fibre link ensured a high-rate secret key transmission with a low quantum bit error ratio for 35 hours. Study first author Dr Jingzhong Yang of the LUH explains: “Comparative analysis with existing QKD systems involving SPS reveals that the SKR achieved in this work goes beyond all current SPS based implementations. Even without further optimisation of the source and setup performance it approaches the levels attained by established decoy state QKD protocols based on weak coherent pulses.” The research outcome shows that seamlessly integrating semiconductor SPSs into realistic, large-scale and high-capacity quantum communication networks is achievable. “Some years ago, we only dreamt of using quantum dots in real-world quantum communication scenarios,” comments Prof. Ding. “Today, we are thrilled to demonstrate their potential for many more fascinating experiments and applications in the future, moving towards a ‘quantum internet’.” The Qurope (Quantum Repeaters using On-demand Photonic Entanglement) project ended in February 2024. MiNet (Large-scale multipartite entanglement on a quantum metrology network) ends in 2027. For more information, please see: MiNet project Qurope project website
Keywords
MiNet, Qurope, quantum, quantum communication, quantum dot, quantum key distribution, single-photon source, cyberthreat, photon