It is believed that quantum computers (QCs) will play a huge role in future computing and communications, including in space technology. Quantum internet (QI) and quantum networks (QN) are one form of application that would involve the quantum technology. In QN a quantum state can be transported between two nodes along with some conventional information. Through the QI, distributed computing can be implemented were multiple QCs operate in parallel. There are multiple challenges that are related to the process of the quantum computing, for example, the rate of quantum encryption keys decreases exponentially due to the fiber attenuation, which means that connecting QCs that are far apart is very hard. Quantum repeaters (QRs) are devices that store quantum states and act as intermediate steps in the quantum communication process. Multiple repeaters can be used, which decreases the quantum communication distance between two individual nodes. Ultimately, the intermediate steps should resolve the distance problem in quantum communications.
When comparing losses in optical fibers and in the vacuum then the latter one is superior, which leads to ideas of using satellites as a platform for QNs. However, this requires complex architectures and protocols to ensure that the QN operates reliably and predictably. The authors of the paper proposes a quantum network backbone that is composed of low Earth orbit (LEO) satellites that are controlled through a modular two-tier control plane (CP), which is based on a software defined network (SDN). The CP are integrated within the ground stations (GSs) and additional control satellites. Each satellite of the constellation performs as a quantum repeater, and all together they build up the data plane (DP). The authors also developed a network layer protocol which meant to creating a E2E entanglement between two GSs. The main contributions of the authors are: design of two-tier CP, a network layer protocol for E2E entanglement between two GSs, and a protocol test that aims to interconnect two QCs ona practical LEO constellation.
To obtain some performance estimates, the proposed design of the architecture was simulated and tested. The authors were able to obtain the time required to obtain entanglement between two GSs using simulated quantum satellite network. During the simulations the GSs were located 20 000 km apart, reference time for the simulation period was one hour, sample being captured every second. During the simulation the number of satellites used to obtain the optimal path varied from four to six. From the results, the authors were able to conclude that larger constellations would provide better results when it comes to the entanglement rate (number of transmitted entangled states per second). As there are more satellites, the probability of having smaller distance between satellites increases, which in turn leads to higher success rate for making an entanglement.
The quantum technologies still have a long way to come so that they can be implemented in real life, but still advances in the theoretical and principal operations can be done as well with the help of simulations. The authors targeted tried to deal with large distance communication between QCs with the help of satellite constellations, and were able to prove that their proposed architecture and protocols were able to perform in simulations.
Sources:
- Chiti, F.; Fantacci, R.; Picchi, R.; Pierucci, L. Towards the Quantum Internet: Satellite Control Plane Architectures and Protocol Design. Future Internet 2021, 13, 196. https://doi.org/10.3390/fi13080196
Presentation: