Abstract
Global-scale quantum communication links will form the backbone of the quantum internet. However, exponential loss in optical fibres precludes any realistic application beyond few hundred kilometres. Quantum repeaters and space-based systems offer solutions to overcome this limitation. Here, we analyse the use of quantum memory (QM)-equipped satellites for quantum communication focussing on global range repeaters and memory-assisted (MA-) QKD, where QMs help increase the key rate by synchronising otherwise probabilistic detection events. We demonstrate that satellites equipped with QMs provide three orders of magnitude faster entanglement distribution rates than existing protocols based on fibre-based repeaters or space systems without QMs. We analyse how entanglement distribution performance depends on memory characteristics, determine benchmarks to assess the performance of different tasks and propose various architectures for light-matter interfaces. Our work provides a roadmap to realise unconditionally secure quantum communications over global distances with near-term technologies.
Highlights
Quantum technologies such as quantum computing[1,2], communication[3,4] and sensing[5,6,7] offer improved performance or new capabilities over their classical counterparts
For connecting ground-based networks, we show that quantum memory (QM) can increase key rates for general line-of-sight distance quantum key distribution (QKD) protocols
We first outline and present results for two quantum repeaters (QRs) protocols for global entanglement distribution. This will be followed by MAQKD protocols in uplink and downlink configurations to increase the key rates in quantum communication within the line-of-sight distance
Summary
Quantum technologies such as quantum computing[1,2], communication[3,4] and sensing[5,6,7] offer improved performance or new capabilities over their classical counterparts. Our approach exploits satellites equipped with QMs to provide entanglement distribution with useful rates[37] (Fig. 1, top) It relies free-space optical repeater links to connect two end stations on on satellites equipped with entangled photon pair sources the ground. Entanglement is distributed between the communicating parties via entanglement swapping operations approach overcomes limitations in purely ground-based repeater networks and trusted satellite relays to outperform previous quantum MA-QKD studies and provide the current best rate-loss scaling for quantum communications over planetary scales. For connecting ground-based networks, we show that QMs can increase key rates for general line-of-sight distance QKD protocols. We exemplify this by analysing a Vienna-Sydney link that is separated by nine ground stations, complete with weather effects. The need for Doppler-shift compensation to ensure indistinguishability of photons in a BSM
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