Researchers at two universities in Germany have demonstrated two quantum entangled atoms separated at opposite ends of a 33-kilometer-long optical fiber. According to the research team, this is an important step towards realizing a practical quantum internet. In the experiment, they entangled two atoms of rubidium in optical traps in two different buildings on the Ludwig-Maximilians University Munich campus. They are separated at both ends of 700 meters of fiber, which is extended to 33 kilometers with additional spools. Each atom is excited by a laser pulse, causing it to emit photons that are quantum entangled with the atom. The photons then travel along the fiber-optic cable, meeting at a receiving station in the middle. The photons are measured jointly there, which makes them entangled, and because they are entangled with their respective atoms, the two atoms are also entangled. While photon entanglement over great distances has been achieved before, this research marks a new distance record for the entanglement of two atoms through an optical fiber, such that the two atoms can act as “quantum memory” nodes.
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