Austrian researchers managed to store quantum information for a long enough period to enable possible global quantum networks based on optical fibres.
The team from the Vienna University of Technology mechanically coupled atoms to glass fibre cables, proving experimentally that glass fibres could store quantum information long enough to entangle atoms hundreds of kilometres apart.
“In our experiment, we have connected two different quantum physical systems”, said Arno Rauschenbeutel, one of the team members. “On one hand, we use fibre-guided light, which is perfect for sending quantum information from A to B, on the other hand, we rely on atoms that are ideal for storing this information.”
By trapping atoms at the distance of about 200nm from a 500nm-in-diameter glass fibre, strong interaction between light and atoms can be implemented. The two systems are then able to exchange quantum information – a process that forms a basis for possible future technologies such as quantum cryptography or quantum teleportation.
One of the biggest challenges of quantum mechanics so far has been in efficient storing and subsequent retrieving of information. The method developed in Vienna offers a convenient solution.
“Our setup is directly connected to a standard optical glass fibre that is nowadays routinely used for the transmission of data”, Rauschenbeutel said. “It will therefore be easy to integrate our quantum-glass-fibre cables into existing fibre communication networks.”
The team has also managed to improve the duration of the period for which the atoms can stay entangled. So far, researchers have been observing that after some time, quantum information is lost as the atoms are affected by the so called ‘decoherence’.
“Using some tricks, we were able to extend the coherence time of the atoms to several milliseconds, in spite of their small distance to the fibre surface”, Rauschenbeutel explained.
As light is the carrier of quantum information, the speed of light sets the upper limit for the distance that can be overcome via entangled atoms.
Even in regular glass-fibre-based telecommunication, signal weakens with the length of the fibre. To overcome this problem, repeater stations are inserted into the network to amplify the weakening optical signal. For quantum networks, special ‘quantum repeaters’ would have to be created, linking several shorter sections into one long quantum connection.
Arno Rauschenbeutel believes the technique developed by his team could serve as a basis for developing such future quantum networks. “By using our combined nano-fibre-atom-system for setting up an optical quantum network including quantum repeaters, one might transmit quantum information and teleport quantum states around the world”, he said.