Abstract
Before global-scale quantum networks become operational, it is important to consider how to evaluate their performance so that they can be built to achieve the desired performance. We propose two practical figures of merit for the performance of a quantum network: the average connection time and the average largest entanglement cluster size. These quantities are based on the generation of elementary links in a quantum network, which is a crucial initial requirement that must be met before any long-range entanglement distribution can be achieved and is inherently probabilistic with current implementations. We obtain bounds on these figures of merit for a particular class of quantum repeater protocols consisting of repeat-until-success elementary link generation followed by joining measurements at intermediate nodes that extend the entanglement range. Our results lead to requirements on quantum memory coherence times, requirements on repeater chain lengths in order to surpass the repeaterless rate limit, and requirements on other aspects of quantum network implementations. These requirements are based solely on the inherently probabilistic nature of elementary link generation in quantum networks, and they apply to networks with arbitrary topology.
Highlights
Progress is being made on building the quantum internet [1,2,3,4], with networks consisting of a handful of nodes currently being developed [5]
These quantities are based on the generation of elementary links in a quantum network, which is a crucial initial requirement that must be met before any long-range entanglement distribution can be achieved and is inherently probabilistic with current implementations
We considered the limitations imposed on quantum networks due to the inherently probabilistic nature of elementary link generation
Summary
Progress is being made on building the quantum internet [1,2,3,4], with networks consisting of a handful of nodes currently being developed [5]. Much work has been devoted to quantifying the performance of quantum repeater networks by using as figures of merit fundamental limits on the rate at which either bipartite or multipartite entanglement and/or a secret key can be generated between points in the network [41,42,43,44,45,46,47,48,49,50]. In these works, perfect quantum repeaters are assumed, and other practical limitations are not explicitly taken into account.
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