Space-Based or Terrestrial-Based Quantum Internet? Pros and Cons
Image: “A hybrid global-quantum-communications network, in which a satellite constellation distributes entangled photon pairs (red wave packets; entanglement depicted by wavy lines) to distant ground stations (observatories) that host multi-mode quantum memories for storage. These stations act as hubs that connect to local nodes (black dots) via fiber-optic or atmospheric links. Using these nearest-neighbor entangled links, via entanglement swapping, two distant nodes can share entanglement. Note that this architecture can support inter-satellite entanglement links as well, which is useful for exploring fundamental physics, and for forming an international time standard.” Image above is from Spooky Action at a Global Distance – Resource-Rate Analysis of a Space-Based Entanglement-Distribution Network for the Quantum Internet [PDF]. Because Quantum is Coming. Qubit.
Why the quantum internet should be built in space
Excerpts and salient points ~
+ How then to build a quantum internet that shares entanglement across the globe? One option is to use “quantum repeaters”—devices that measure the quantum properties of photons as they arrive and then transfer these properties to new photons that are sent on their way. This preserves entanglement, allowing it to hop from one repeater to the next. However, this technology is highly experimental and several years from commercial exploitation.
Khatri and co say that a constellation of similar satellites is a much better way to create a global quantum internet. The key is that to communicate securely, two ground stations must be able to see the same satellite at the same time so that both can receive entangled photons from it..
+ So another option is to create the entangled pairs of photons in space and broadcast them to two different base stations on the ground. These base stations then become entangled, allowing them to swap messages with perfect secrecy.
+ Nevertheless, a space-based quantum internet significantly outperforms ground-based systems of quantum repeaters, say Khatri and co. Repeaters would have to be spaced at intervals of less than 200 kilometers, so covering long distances would require large numbers of them. This introduces its own set of limitations for a quantum internet.
+ “We thus find that satellites offer a significant advantage over ground-based entanglement distribution,” say Khatri and co.
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