Tech
Quantum Internet Test Links Three Cities
Researchers have transmitted entangled photons over 500 kilometers of fiber connecting three cities, setting a new record for fidelity in a quantum network link. The demonstration brings a practical quantum internet closer, with potential applications in ultra-secure communication and distributed quantum computing.
Illustration: Clear News
Physicists have demonstrated a quantum internet link spanning three cities and 500 kilometers of fiber, transmitting entangled photons with record fidelity, the research team announced this week.
The experiment connected nodes in three metropolitan areas through standard commercial fiber optic cable. By sending pairs of entangled photons across the full distance and confirming their quantum correlation at each endpoint, the team proved that quantum information can survive a journey long enough to cover real-world regional networks.
Previous demonstrations were limited to shorter distances or required laboratory conditions. This test used existing fiber infrastructure, a critical step toward making quantum networks practical rather than theoretical.
"Every time we extend the distance, we learn something new about how entanglement behaves in the wild," said the project's lead researcher in a statement. "This is the first time we've seen this level of fidelity over hundreds of kilometers of ordinary fiber."
The key achievement was fidelity, a measure of how faithfully the quantum state arrives at its destination. The team reported fidelity above 90 percent, a threshold that many quantum protocols require to function. Earlier long-distance attempts had degraded badly at similar ranges.
Why a quantum internet matters
Quantum networks promise communication that is fundamentally secure. Because observing a quantum state changes it, any eavesdropper intercepting an entangled link would be detected immediately. Banks, governments, and hospitals could use such links to exchange data with security guaranteed by physics rather than mathematics.
The second application is distributed quantum computing. Linking smaller quantum processors over a quantum network could let them work together as a single larger machine, potentially sidestepping the difficulty of building very large processors in one place.
What comes next
The researchers say the next milestone is adding quantum memory at each node, which would allow the network to store entangled states and route them on demand, more like today's internet. They estimate that capability is three to five years away.
Industry observers are watching closely. Several telecommunications companies have begun funding quantum networking research, betting that early infrastructure investments will pay off as the technology matures.
The full results will be presented at a quantum information conference in November, and a preprint paper is expected to be posted publicly within weeks.
