0310097v4

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The Minimum Distance Problem for Two-Way Entanglement Purification

Andris Ambainis, Daniel Gottesman

abstract: Entanglement purification takes a number of noisy EPR pairs and processes them to produce a smaller number of more reliable pairs. If this is done with only a forward classical side channel, the procedure is equivalent to using a quantum error-correcting code (QECC). We instead investigate entanglement purification protocols with two-way classical side channels (2-EPPs) for finite block sizes. In particular, we consider the analog of the minimum distance problem for QECCs, and show that 2-EPPs can exceed the quantum Hamming bound and the quantum Singleton bound. We also show that 2-EPPs can achieve the rate k/n = 1 - (t/n) \log_2 3 - h(t/n) - O(1/n) (asymptotically reaching the quantum Hamming bound), where the EPP produces at least k good pairs out of n total pairs with up to t arbitrary errors, and h(x) = -x \log_2 x - (1-x) \log_2 (1-x) is the usual binary entropy. In contrast, the best known lower bound on the rate of QECCs is the quantum Gilbert-Varshamov bound k/n \geq 1 - (2t/n) \log_2 3 - h(2t/n). Indeed, in some regimes, the known upper bound on the asymptotic rate of good QECCs is strictly below our lower bound on the achievable rate of 2-EPPs.

Medatada:

oai_identifier:

oai:arXiv.org:quant-ph/0310097

categories:

quant-ph

comments:

10 pages, LaTeX. v2: New title, minor corrections and clarifications, some new references. v3: One more small correction. v4: More small clarifications, final version to appear in IEEE Trans. Info. Theory

doi:

10.1109/TIT.2005.862089

arxiv_id:

quant-ph/0310097

journal_ref:

IEEE Trans. Info. Theory vol. 52, issue 2, 748-753 (2006)

created:

2003-10-14

updated:

2005-10-13

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