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Some powerful rulers of the world may dream of the possibility to get in touch with their colleagues on different continents unnoticed by friends or foes. Someday, new quantum technologies could allow for making these wishes come true. Physicists around the world are working on the realization of large scale quantum networks in which single light quanta transfer (secret) quantum information to stationary nodes at large distances. Such quantum networks' fundamental building blocks are, for example, quantum repeaters that counteract the loss of quantum information over large distances, or quantum logic gates that are necessary for processing quantum information.
Now, a team of scientists around Professor Gerhard Rempe, director at the Max Planck Institute of Quantum Optics and head of the Quantum Dynamics Division, has demonstrated the feasibility a new concept for a quantum gate. Here, photons impinging on an optical cavity mediate an interaction between two atoms trapped inside. This interaction is the basis for performing characteristic gate operations between the atoms, for example the operation as a CNOT gate or the generation of entanglement. The new method offers a variety of advantages: for example, the gate operations take place within microseconds which is an asset for quantum information processing. Also, the gate mechanism can be applied to other experimental platforms, and the two-atom gate can serve as a building block in a quantum repeater.
Core - Element - Experiment - Resonator - High-reflection
Core element of the experiment is an asymmetric high-finesse optical resonator, consisting of a high-reflection mirror (left) and a mirror with a finite transmission (right). Two electrically neutral rubidium atoms are trapped in the centre of the cavity. Each atom carries a qubit, i.e. quantum information that is encoded in the superposition of two stable ground states which correspond to the classical bits "0" and "1." "One of the ground states is in resonance with the...
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