How the Quantum Internet is Being Built

Synopsis

A quantum internet would do something no classical network can: share entanglement, a uniquely quantum link that makes two particles behave as one system, however far apart they are. That could join today's small quantum computers into larger machines, merge distant telescopes into one far-seeing instrument, and put a lock on communications that even a quantum computer couldn't pick. But entanglement travels on single photons, and optical fibre loses about half of them every 15 km. Classical signals can simply be amplified along the way, but amplifying means copying, and quantum information cannot be copied. A lost photon is gone for good. To remedy this, satellites send photons mostly through empty space, where nothing absorbs them; quantum repeaters, on the other hand, are distributed nodes along the route that keep losses from compounding over the full distance. I'll show how these pieces fit together, and what it will take to go from links between cities to a network spanning the planet.