Kavli Affiliate: Stephanie Wehner
| First 5 Authors: Álvaro G. Iñesta, Bethany Davies, Sounak Kar, Stephanie Wehner,
| Summary:
Entanglement buffers are systems that maintain high-quality entanglement,
ensuring it is readily available for consumption when needed. In this work, we
study the performance of a two-node buffer, where each node has one long-lived
quantum memory for storing entanglement and multiple short-lived memories for
generating fresh entanglement. Newly generated entanglement may be used to
purify the stored entanglement, which degrades over time. Stored entanglement
may be removed due to failed purification or consumption. We derive analytical
expressions for the system performance, which is measured using the
entanglement availability and the average fidelity upon consumption. Our
solutions are computationally efficient to evaluate, and they provide
fundamental bounds to the performance of purification-based entanglement
buffers. We 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. A key finding is that simple purification
protocols, such as DEJMPS, often provide superior buffering performance
compared to protocols that maximize output fidelity.
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