Researchers at Princeton University in the US have made a key step towards realizing scalable quantum networks thanks to a rare-earth element: erbium. Erbium is good at emitting and absorbing photons at wavelengths used in the telecommunications industry, which is an advantage because these photons can travel long distances with little attenuation in standard optical fibres. Harnessing this strength in the quantum realm has been a challenge, but the Princeton team managed to coax an erbium-based device into emitting identical photons – a prerequisite for quantum repeaters to share quantum information across vast distances.

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