Fig. 5: Performance of repeaters based on nitrogen-vacancy (NV) centres in diamond.

a Fidelity and entanglement distribution rate achieved with near-term and 10× improved hardware (Supplementary Note 4) with the SWAP-ASAP protocol. Dashed line represents classical fidelity threshold of 0.5. We observe that for near-term hardware, the use of three repeaters yields worse performance in terms of fidelity than the no-repeater setup. For improved hardware we observe (i) that for ~0–750 km, repeaters improve upon rate by orders of magnitude while still producing entanglement (fidelity > 0.5), while (ii) for ~750–1500 km, repeaters outperform in both rate and fidelity. b, c Fidelity and rate achieved without and with repeaters (1, 3 or 7 repeaters) as function of a hardware improvement factor (Methods, section ‘How we choose improved hardware parameters’) for two typical distances from both distance regime (i) and (ii), for two protocols SWAP-ASAP and NESTED-WITH-DISTILL. For the repeater case, only the best-performing number-of-repeaters and protocol in terms of achieved fidelity is shown in (b), accompanied by its rate in (c). Each data point represents the average over (a) 200 and (b) 100 runs. Standard deviation is smaller than dot size.