Matter-matter entanglement at a distance

Because of its strange consequences the quantum mechanical phenomenon of entanglement has been called “spooky action at a distance” by Albert Einstein. For several years physicists have been developing concepts how to use this phenomenon for practical applications such as absolutely safe data transmission. For this purpose, the entanglement which is generated in a local process has to be distributed among remote quantum systems. A team of scientists around Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics and head of the Quantum Dynamics Division, has now demonstrated that two remote atomic quantum systems can be prepared in a shared “entangled” state (Physical Review Letters, Advance Online Publication, 26 May 2011): one system is a single atom trapped in an optical resonator, the other one a Bose-Einstein condensate consisting of hundreds of thousands of ultracold atoms. With the hybrid system thus generated, the researchers have realized a fundamental building block of a quantum network.