Abstract
Entanglement buffers are systems that maintain high-quality entanglement, ensuring it is readily available for consumption when needed. We study the performance of a two-node buffer, where each node has one long-lived quantum memory for entanglement storage and multiple short-lived memories for generation. Freshly generated entanglement may be used to purify stored entanglement, which degrades over time. Stored entanglement may be removed due to consumption or failed purification. We derive analytical expressions for the entanglement availability and the average fidelity upon consumption. Our solutions are computationally efficient and provide fundamental bounds to the performance of purification-based entanglement buffers. We also show that purification must be performed as frequently as possible to maximise the average fidelity of entanglement upon consumption, even if this often leads to the loss of high-quality entanglement due to purification failures. Moreover, we obtain heuristics for the design of good purification policies in practical systems.
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Data availability
No data is needed to reproduce our results, since all results in this manuscript are analytical. The code used to perform the analysis and generate all the plots shown in this paper can be found in the following GitHub repository: https://github.com/AlvaroGI/buffering-1GnB. This repository also includes a discrete-event simulator of a 1G$n$B system that we used to validate our analytical results.
Code availability
The code used to perform the analysis and generate all the plots shown in this paper can be found in the following GitHub repository: https://github.com/AlvaroGI/buffering-1GnB. This repository also includes a discrete-event simulator of a 1GnB system that we used to validate our analytical results.
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Acknowledgements
We thank S. Jansen, C. Cicconetti, P. Kaku, and J. van Dam for discussions and feedback. Á.G.I. acknowledges financial support from the Netherlands Organisation for Scientific Research (NWO/OCW), as part of the Frontiers of Nanoscience programme. B.D. acknowledges financial support from a KNAW Ammodo Award (S.W.). S.W. acknowledges support from an NWO VICI grant.
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B.D. and Á.G.I. conceived and defined the project. B.D. and S.K. proved Theorems 1 and 2. Á.G.I. and B.D. proved Propositions 1 and 2. Á.G.I. carried out the analysis from “Monotonic performance” and “Discussion”, and coded the discrete-event simulation (used to validate analytical results). Á.G.I. and B.D. wrote this manuscript. S.W. supervised the project.
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Iñesta, Á.G., Davies, B., Kar, S. et al. Entanglement buffering with multiple quantum memories. npj Quantum Inf (2026). https://doi.org/10.1038/s41534-025-01161-3
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DOI: https://doi.org/10.1038/s41534-025-01161-3
