Long-distance relays for quantum data
Thus the method reported by the Munich researchers could enable construction of a “quantum repeater”. By acting as a relay, this effectively sidesteps the problem of signal loss, and allows the propagation of quantum information over much longer distances.
To build an extensive network based on entanglement, one must be able to measure states of particles that are widely separated. The present limit for photons is some 140 km, because of losses due to absorption on the way. Therefore some sort of "relay station" which is able to store quantum information is necessary. Researchers led by LMU physicist Julian Hoffmann, together with colleagues at the MPI for Quantum Optics, have now achieved a decisive breakthrough. They have managed to entangle two rubidium atoms held in optical traps 20 meters apart. Not only that, the system sends a signal which “announces” that entanglement has been achieved.
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