Towards a global quantum network

TL;DR

Directly distributing quantum states over thousands of kilometers is limited by optical loss and the no-cloning theorem. The paper discusses combining satellite links with quantum memories and repeaters, alongside milestones and experiments toward a global network. Existing demonstrations and proposed architectures indicate that this vision is within reach, while important engineering challenges remain.

• Problem

  Optical fiber loss makes direct single-photon transmission over thousands of kilometers impractical, while quantum signals cannot be amplified because of the no-cloning theorem.

• Method

  The paper examines combining satellite links, quantum memories, and entanglement swapping to distribute entanglement across terrestrial and global distances.

• Results

  Experiments have demonstrated teleportation between memories over 150 m of fiber, photon teleportation onto a solid-state memory over 25 km, and a repeater-link-scale non-locality test over 1.3 km.

• Takeaways & Limitations

  Satellite links and quantum memories can complement each other by creating loss-free ground-station-to-city links and supporting entanglement over truly global distances.

• Takeaways & Limitations

  Important milestones remain, including 100 km repeater links, connecting links by entanglement swapping, and exceeding direct-transmission rates; satellite links also suffer intermittency, low rates, and photon loss.