Scientists Send Unhackable Quantum Keys Across Record 120 Kilometers
Breakthrough quantum encryption system maintained continuous operation for six hours while achieving highest secure key rates yet for this technology.
Scientists have achieved a major milestone in quantum cryptography by successfully demonstrating an ultra-secure quantum key distribution system that operated continuously across more than 120 kilometers of optical fiber. The breakthrough experiment, conducted by an international research team from universities in Germany and China, represents one of the most stable and long-distance quantum encryption demonstrations to date.
The quantum key distribution system utilized semiconductor quantum dots, tiny solid-state devices that can generate high-quality single photons on demand for quantum communication. These quantum dots produced bright, highly pure single photons at an operating rate of approximately 76 MHz, providing the foundation for the secure transmission of encryption keys that would be virtually impossible for hackers to intercept or decode without detection.
A critical innovation in the experiment was the use of time-bin encoding, a technique that stores quantum information in the arrival times of individual photons. This approach proved especially valuable for long-distance quantum communication because it demonstrates natural resistance to many environmental disturbances that typically disrupt fiber optic networks. The researchers successfully transmitted quantum signals between an encoder and decoder separated by the 120-kilometer fiber link.
The system maintained remarkable stability throughout more than six hours of continuous operation without requiring manual adjustments, a crucial requirement for practical quantum communication networks. Even after the quantum signals traveled through 120 kilometers of standard optical fiber, the system kept average quantum bit error rates below 11 percent while achieving secure key rates of approximately 15 bits per second under realistic operating conditions.
The achievement represents a significant step toward building practical quantum internet infrastructure that could provide unprecedented security for sensitive communications. The researchers noted that their quantum dot-based approach offers particular promise for integration into real-world quantum key distribution systems, potentially enabling secure communications across intercity distances for applications ranging from financial transactions to government communications.
