Researchers at the National Institute of Standards and Technology have successfully transmitted entangled photons across 62 kilometers of existing above-ground fiber-optic infrastructure. This experiment serves as a critical test for the future of quantum networking, proving that these connections can remain stable even when exposed to environmental disturbances like wind and temperature fluctuations.
Quantum networks rely on entanglement, a phenomenon where particles share a unified state regardless of the distance between them. While this holds promise for highly secure communications and synchronized quantum sensors, the fragility of these states makes transmission difficult. Unlike classical internet signals, quantum information is sensitive to the physical state of the fiber cables. The outdoor lines used in this study are subject to constant expansion, contraction, and movement, which historically creates significant noise that disrupts data.
To overcome these issues, the research team utilized real-time polarization stabilization technology provided by the company Qunnect. This system sent reference light beams through the same fiber to monitor how the cable was distorting the signals. By applying the inverse of these transformations to the entangled photons, the team maintained the necessary quantum states for the duration of the test.
During a 24-hour observation period, the team achieved a transmission rate of 1,500 entangled photons per second. The system maintained entanglement for 92.8% of the total time, marking a major milestone for deploying quantum protocols on standard, pre-existing telecommunications hardware. This proves that expensive, purpose-built networks may not be the only way to build a functional quantum future.