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International Conference on Quantum Information

DLCZ Quantum Repeaters: Rate and Fidelity Analysis

Jeyran Amirloo, Mohsen Razavi, A. Hamed Majedi

Published Jan 1, 2008• 3 citations
Publisher

Abstract

The fidelity and the rate of entanglement generation for the DLCZ entanglement-swapping protocol are evaluated. We find the distance beyond which DLCZ repeaters outperform single DLCZ links by accounting for loss, multiple-excitation, and self-purification effects.
DOI
10.1364/icqi.2008.jmb54

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A feasible route toward implementing long-distance quantum key distribution (QKD) systems relies on probabilistic schemes for entanglement distribution and swapping as proposed in the work of Duan, Lukin, Cirac, and Zoller (DLCZ) [Nature (London) 414, 413 (2001)]. Here, we calculate the conditional throughput and fidelity of entanglement for DLCZ quantum repeaters by accounting for the DLCZ self-purification property in the presence of multiple excitations in the ensemble memories as well as loss and other sources of inefficiency in the channel and measurement modules. We then use our results to find the generation rate of secure key bits for QKD systems that rely on DLCZ quantum repeaters. We compare the key generation rate per logical memory employed in the two cases with and without a repeater node. We find the crossover distance beyond which the repeater system outperforms the nonrepeater one. That provides us with the optimum internode distancing in quantum repeater systems. We also find the optimal excitation probability at which the QKD rate peaks. Such an optimum probability, in most regimes of interest, is insensitive to the total distance.
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We analyze the efficiency and scalability of the DLCZ protocol for quantum repeaters through experimentally accessible measures of entanglement like concurrence and CHSH inequality, taking into account the state degradation due to various imperfections of the stored entangled states. We also provide a more accurate estimate for the average time required to succeed in each step of the protocol. The minimum purity analysis and the new time estimates are then combined to trace the perspectives for implementation of the DLCZ protocol in present-day laboratory setups.