Hannover team sends a four-qubit state through 29 km of city fiber
A Hannover team transmitted a four-qubit cluster state through 29.5 kilometers of partly deployed optical fiber, and its result reached peer-reviewed publication in a newly published paper. The experiment used time-bin encoding to carry a complex entangled state through fiber compatible with telecommunications infrastructure. It is a research demonstration, not an operating quantum network or proof of reliable service at scale.
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An entangled state crosses city fiber
A Hannover team transmitted a four-qubit cluster state through approximately 29.5 km of partly deployed optical fiber. Leibniz University Hannover announced the result on October 1, and Quantum Zeitgeist reported the same demonstration. The peer-reviewed Light: Science & Applications paper was published that day. It extends a result described in a June conference abstract by providing the full experimental report; it is not evidence that a commercial quantum network is operating.[1], [2], [3]
Two photons carried four qubits
The experiment encoded four qubits in two photons using distinct time bins. One photon remained in the laboratory; its partner travelled through a campus fiber loop and an added laboratory spool. The optical path totaled about 29.5 km, but both processing nodes were in the same laboratory. The researchers used a timed generation method and a configurable time-bin beam splitter to prepare and measure the cluster state. This arrangement avoids treating the demonstration as a link between autonomous distant processors.[1]
Transmission has a measurable limit
The paper reports measurements consistent with genuine multi-qubit entanglement after transmission and elementary measurement-based processing steps. Quantum Zeitgeist identifies the same test as a step toward future quantum networking. Yet loss of one photon also removes both qubits encoded on it, while component losses and unwanted mixing between time bins constrain performance. The result demonstrates compatibility with ordinary optical fiber; it does not establish fault tolerance, universal computation or reliable service at scale.[1], [3]
