Ring, Ring: 'Earth? It's space calling, on the quantum line'

The distribution of quantum entanglement, especially across vast distances, holds important implications for quantum teleportation and communication networks. Yet, efforts to entangle quantum particles, essentially "linking" them together over long distances, have been limited to 100 km or fewer, mostly because the entanglement is lost as they are transmitted along optical fibers, or through open space on land.

One way to overcome this issue is to break the line of transmission into smaller segments and repeatedly swap, purify and store quantum information along the optical fiber. Another approach to achieving global-scale quantum networks is making use of lasers and satellite-based technologies.

Using the Chinese satellite Micius, launched last year and equipped with specialized quantum tools, Juan Yin et al. demonstrate the latter feat. The Micius satellite was used to communicate with three ground stations across China, each up to around 1,200 km apart.

The separation between the orbiting satellite and these ground stations varied from 500 to 2,000 km.

A laser beam on the satellite was subjected to a beam splitter, which gave the beam two distinct polarized states.

One of the spilt beams was used for transmission of entangled photons, while the other was used for photon receipt. In this way, entangled photons were received at the separate ground stations, more than 1,000 km apart.