This is a report for the U.S. Department of Energy outlining development toward the Quantum Internet (QI). The QI depends on a phenomenon known as quantum entanglement, whereby a change of state in one particle is mirrored by a second particle, no matter how far distant. Einstein called it "spooky action at a distance". So it's a means of instantaneous information transmission. The speed would be limited only by how fast we can generate and read changes of state. This report (38 page PDF) is fairly technical, but the first 11 pages are accessible and will give you the general idea. Via Protocol.