Toward a Practical Quantum Repeater
Extending Quantum Entanglement Across Town
+ A team of German researchers has stretched the distance quantum information can travel from stationary quantum memory to optical telecom pulse. The group’s new experiment transfers the information contained in a single quantum bit from an atomic state to a single photon, then sends it through some 20 kilometers of fiber optic cable.
“One of the grand goals is a quantum network, which then would link together different quantum computers,” says Harald Weinfurter, professor of physics at Ludwig Maximilian University of Munich, Germany. “And if we can establish entanglement between many such segments, then we can link all the segments together. And then link, in an efficient manner, two atoms over a really long distance.”
+ This finding begins to extend the distance over which quantum systems (including quantum computers and quantum communications hubs) can be physically separated while still remaining connected. It also serves as a milestone on the road toward a so-called quantum repeater, which would broadly expand the footprint of quantum technologies toward regional, national, or even international connectivity.
+ [A]s quantum computer makers today know all too well, the challenge of error correction will rear its head. As with quantum computer error correction, entanglement purification for a quantum communication system like this is not an easy challenge to overcome. But it’s a necessary step if present-day technologies are to be scaled up into a system that can transmit quantum entanglement from one stationary qubit to another at dozens or hundreds of kilometers distance or more.
+ “In the whole process, we lose the quality of the entangled states,” Weinfurter said. “Then we have to recover this. There are lots of proposals how to do this. But one has to implement it first.”
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