(Phys.org) Researchers from Sorbonne University in Paris have achieved a highly efficient transfer of quantum entanglement into and out of two quantum memory devices. This achievement brings a key ingredient for the scalability of a future quantum internet.
A quantum internet that connects multiple locations is a key step in quantum technology roadmaps worldwide. In this context, the European Quantum Flagship Programme launched the Quantum Internet Alliance in 2018.
One major challenge in building large-scale quantum networks is the ability to generate such correlations between distant nodes. In principle, this challenge can be overcome if entanglement is reliably stored in quantum memory devices. By splitting the long distance into several shorter segments, it is possible to create entanglement between the ends of these elementary links, and then connect them until both initial nodes are entangled. The quantum memory devices store the entanglement, ensuring that entanglement has been created over all the segments before performing the connections. This protocol is known as a quantum repeater.
Prof. Julien Laurat and his team at Kastler Brossel Laboratory (Sorbonne Université, CNRS, ENS-Université PSL, Collège de France) reported a long-awaited step for this endeavor. They have demonstrated the storage and retrieval of entangled light beams into two quantum memory devices, with an overall efficiency as high as 85%. This value constitutes more than a three-fold increase relative to prior works in the field.
“This achievement is the result of 10 years of experimental developments in our lab. It now opens the path to further investigation as many potential network architectures assume such efficiency value for scalability,” says Félix Hoffet, a Ph.D. student at LKB and one of the leading authors of the paper.
The work reported in Optica is a stepping stone for further investigations. However, the path for building large-scale networks is still paved with challenges. For example, efficient quantum memory devices also need to have long storage times in order to create entanglement faster than it is lost. This critical feature can also come with the ability to store different information in parallel.

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