In this paper, quantum networking was the focus. Here the researchers are looking at a proposed space-borne quantum memories for global networking.
First quantum technology is a class of technology that works by using the principles of quantum mechanics (the physics of sub-atomic particles), including quantum entanglement and quantum superposition. It gives an insight of quantum technologies such as computing, communication, and sensing that it offers improved performance or new capabilities over classical counterparts. As one of the first applications of quantum communication, quantum key distribution (QKD) has been leading the emergence of quantum information technologies and establishes the foundation for wide-scale quantum networking.
The paper talks about conventional optical repeaters that cannot be used with QKD as quantum information cannot be cloned ideally. This in turn aids unconditional security against eavesdropping. The long distance fiber QKD links employ trusted nodes that effectively relay a secure key between the two ends. Trusted nodes are assumed to be safe from 3rd parties and are potential areas for weakness. The trusted nodes are also unsuitable for the long-range distribution of entanglement, hence the need to overcome the terrestrial limits (~ 1000km) of direct quantum transmission.
More advanced method describes that for movement beyond this terrestrial limit would need the use of intermediate nodes that would be equipped with memories, that is quantum memories (QMs) or quantum repeaters (QRs), which do not need to be assumed free from malicious control. Therefore to exploiting the assistance of the QRs to divide the transmission link into smaller segments, it is then possible to overcome the fundamental rate-loss scaling for direct transmission, though at the expense of many intermediate repeater nodes.
For this paper, it was proposed that a hybrid satellite-assisted would be used for entanglement distribution with useful rates. It would rely on a satellite equipped with an entangled photon pair sources communicating with the memory nodes located in ground stations.
In this case, the researchers outlined and presented results for two QR protocols for global entanglement distribution. This will be followed by Memory assisted quantum key distribution (MA-QKD) protocols in uplink and downlink configurations to increase the key rates in quantum communication within the line of sight distance. The quantum memories are used as storage devices to help increase the rate of bell state measurements (BSMs) that form the backbone of most MDI protocols. Then it the results were compared with known results that use ground-based schemes. The focus was in LEO to directly compare the results with existing experimental demonstrations.
Conclusions: Satellite equipped with QMs provide orders of magnitude of faster entanglement distribution rates than existing protocols based on the fiber-based repeaters or space system without QMs. The idea of the project or paper gives a roadmap to realize unconditionally secure quantum communications over global distances with near-term technologies.
Sources: Mustafa Gundogan, Jasminder S. Sidhu, Victoria Henderson, Luca Mazzarella, Janik Wolters, Daniel K, Markus Krutzik. (2021). Proposal for space-borne quantum memories for global quantum networking. https://www.nature.com/articles/s41534-021-00460-9