Realistic parameter regimes for a single sequential quantum repeater node

The goal of a quantum repeater is to be able to communicate more efficiently than it is possible without a quantum repeater. In particular, it is natural to compare the rate at which one can generate secret key with an implementation of a quantum repeater and the theoretical maximum rate without one. By modeling such a repeater implementation, it is possible to find parameter regimes where repeaters would give a benefit over direct communication. Here, we model a specific, but general, setup for a repeater which can be implemented using, for example, nitrogen-vacancy centers. Furthermore, we also introduce three new tools to assess the performance of repeaters. The first of these tools is a series of benchmarks based on finite-energy considerations and to what one considers as losses in the setup. The second tool is the introduction of a cut-off, which reduces the effect of decoherence in systems such as nitrogen-vacancy centers by implementing a maximum on the allowed storage time. Finally, we analyze the repeater setup when advantage distillation is used, which is a more advanced type of classical post-processing. Using these tools, we find realistic parameters for which it is possible to beat the mentioned benchmarks, guiding the way towards implementing quantum repeaters.