MUNICH, Germany Scientists from Austria, China and Germany have implemented a stable quantum repeater. The device has the potential to obtain a central function in future quantum effect-based communication networks.
The quantum repeater could counteract the signal attenuation on long-distance data transfers, the researchers said. While in electronic networks, amplifiers and filters that regenerate the signal after certain distances are standard technology, the situation is different in quantum data transfer. In quantum physics, the same fundamental principles that make the communications process absolutely secure prevent that the signal can be amplified without total loss of the information content.
The researchers from the Vienna university, the University of Science and Technology of China and the Heidelberg university now have succeeded in designing an array that combines quantum information storage and signal conditioning. The approach is based on the so called BDCZ protocol (Briegel, Dür, Cirac, Zoller), but the combination of this protocol with a device that can store quantum information is the central challenge, the researchers describe in a press release.
While the method described is "intrinsically stable", it looks like it is still very far from an industrial use: The researchers created two ensembles of a million ultra-cold atoms at a temperature of 100 microKelvin (about minus 273.15 degrees Celsius) in a magneto-optical trap. Then in each of the ensembles, a common quantum status of the atoms with a photon has been entangled and in a complicated process a so called entanglement interchange has been carried out. Since the atomic quantum status can be transferred to other photons at a later point in time, the information can be read, verified and used again.
The researchers believe that the elements demonstrated can be expanded to a quantum network. "For a robust application, however, the quality of the quantum storage as well as the atom-photon entanglement need to be further improved," the scientists say in a statement.