The research, published in Light Science and Applications, marks a significant milestone in quantum communication technology. The core of this breakthrough lies in the use of semiconductor quantum dots (QDs), often referred to as artificial atoms. These QDs have shown great potential for generating quantum light, which is crucial for quantum information technologies. In their experiment, the researchers connected Hannover and Braunschweig via an optical fiber network, a setup they called the “Niedersachsen Quantum Link.”
This intercity experiment involved a fiber optic cable approximately 79 kilometers long that linked the Leibniz University of Hannover and Physikalisch-Technische Bundesanstalt Braunschweig. Alice, located at LUH, prepared single photons encrypted in polarization. Bob, stationed at PTB, used a passive polarization decoder to decrypt the polarization states of the received photons.
This setup represents the first quantum communication link in Lower Saxony, Germany.
The team achieved stable and rapid transmission of secret keys, demonstrating that positive secret key rates (SKRs) are feasible for distances up to 144 kilometers, corresponding to a 28.11 dB loss in the laboratory. They ensured a high-rate secret key transmission with a low quantum bit error ratio (QBER) for 35 hours based on this deployed fiber link.
Dr. Jingzhong Yang, the first author of the study, highlighted that their achieved SKR surpasses all current single-photon source (SPS) based implementations. Even without further optimization, their results approach the levels attained by established decoy state QKD protocols using weak coherent pulses.
Beyond QKD, quantum dots offer significant potential for other quantum internet applications, such as quantum repeaters and distributed quantum sensing. These applications benefit from the inherent ability of QDs to store quantum information and emit photonic cluster states. This work underscores the feasibility of integrating semiconductor single-photon sources into large-scale, high-capacity quantum communication networks.
Quantum communication leverages the quantum characteristics of light to ensure messages cannot be intercepted. “Quantum dot devices emit single photons, which we control and send to Braunschweig for measurement. This process is fundamental to quantum key distribution,” explained Professor Ding. He expressed excitement about the collaborative effort’s outcome, noting, “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.’”
The advancement of QKD with semiconductor quantum dots represents a major step forward in the quest for secure communication in the age of quantum computing. This breakthrough holds promise for more robust and expansive quantum networks, ensuring the confidentiality and security of sensitive information against the evolving landscape of cyber threats.
As the world continues to advance towards more interconnected digital environments, the necessity for secure communication becomes ever more critical. The pioneering work of these scientists not only showcases the potential of QKD but also paves the way for future innovations in quantum communication and beyond.
