Quantum Key Distribution (QKD) is a technology that utilizes the unique properties of quantum physics to secure data transmission, as conventional encryption methods are becoming vulnerable due to the rise of quantum computers. In a groundbreaking development, a team of scientists in Germany has achieved the first intercity QKD experiment using a deterministic single-photon source, which could revolutionize secure data transmission.
The experiment, known as the ‘Niedersachsen Quantum Link,’ was conducted between the Leibniz University of Hannover (Alice) and Physikalisch-Technische Bundesanstalt (PTB) Braunschweig (Bob), connecting the two cities via optical fiber over a distance of approximately 79 km. The team was led by Professor Fei Ding from Leibniz University of Hannover, Professor Stefan Kück from PTB, Professor Peter Michler from University of Stuttgart, and other co-workers.
Alice prepares single photons that are encrypted in polarization, while Bob decrypts the polarization states of the received single photons using a passive polarization decoder. The researchers have achieved stable and fast transmission of secret keys, with positive secret key rates (SKRs) determined achievable for distances up to 144 km in the laboratory. They also ensured a high-rate secret key transmission with a low quantum bit error ratio (QBER) for 35 hours based on this deployed fiber link.
The use of semiconductor quantum dots (QDs) in this experiment offers great prospects for other quantum internet applications, such as quantum repeaters and distributed quantum sensing, as they allow for inherent storage of quantum information and can emit photonic cluster states. The outcome of this work underscores the viability of seamlessly integrating semiconductor single-photon sources into realistic, large-scale, and high-capacity quantum communication networks.
Professor Fei Ding explained, “We work with quantum dots, which are tiny structures similar to atoms but tailored to our needs. For the first time, we used these ‘artificial atoms’ in a quantum communication experiment between two different cities.” Ding further added, “Some years ago, we only dreamt of using quantum dots in real-world quantum communication scenarios. Today, we are thrilled to demonstrate their potential for many more fascinating experiments and applications in the future, moving towards a ‘quantum internet.'”
More information about this research can be found in the article titled “High-rate intercity quantum key distribution with a semiconductor single-photon source,” published in Light: Science & Applications.
