Researchers at the Niels Bohr Institute in Copenhagen have achieved a breakthrough in quantum communication by creating a device that sends single photons through existing fiber optic networks at telecommunications wavelengths, a feat that scientists once considered impossible. The advance, published in Nature Nanotechnology, removes one of the biggest obstacles to building a global quantum internet that would make eavesdropping physically detectable and communications fundamentally secure.
The core of the breakthrough lies in electrically controlled quantum dots embedded in a nanophotonic circuit. These quantum dots produce over 40 million nearly identical, coherent single photons per second in the telecom O-band, with emission quality only eight percent broader than the fundamental physical limit. Previous quantum dot devices operated at around 930 nanometer wavelengths, far short of the 1,260 nanometer threshold required for compatibility with the global telecommunications fiber infrastructure that already spans millions of kilometers.
The significance of operating at telecom wavelengths cannot be overstated. It means that quantum-secured communications can be deployed on the same optical fiber cables that currently carry conventional internet traffic, without requiring new dedicated infrastructure. Any attempt to intercept these single-photon transmissions would disturb the quantum state of the photons, immediately alerting both sender and receiver to the intrusion. This property makes the system fundamentally different from classical encryption, which relies on mathematical complexity that future quantum computers could potentially defeat.
The research team also demonstrated quantum key distribution over a field-installed fiber link, proving that the technology works outside laboratory conditions. An international collaboration between the Niels Bohr Institute and researchers in Germany and China separately achieved secure quantum key distribution over 127 kilometers using similar quantum dot technology, showing that the approach can scale to meaningful distances for real-world deployment.
Industry experts say the breakthrough could accelerate the timeline for practical quantum networks from decades to years. Governments and financial institutions have been among the most vocal advocates for quantum-secured communications, given the sensitive nature of the data they transmit. With this advance, the researchers have demonstrated that the fundamental building blocks for a quantum internet now exist and can operate on infrastructure already in place worldwide. The team is now working on increasing the transmission distance and developing multiplexing techniques to handle multiple quantum channels simultaneously.
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