Physics – Quantum Physics
Scientific paper
2006-07-05
IEEE Trans. Info. Theory 54, 9, 4208-4217 (2008)
Physics
Quantum Physics
10 pages, 4 figures
Scientific paper
10.1109/TIT.2008.928269
We present an upper bound for the quantum channel capacity that is both additive and convex. Our bound can be interpreted as the capacity of a channel for high-fidelity quantum communication when assisted by a family of channels that have no capacity on their own. This family of assistance channels, which we call symmetric side channels, consists of all channels mapping symmetrically to their output and environment. The bound seems to be quite tight, and for degradable quantum channels it coincides with the unassisted channel capacity. Using this symmetric side channel capacity, we find new upper bounds on the capacity of the depolarizing channel. We also briefly indicate an analogous notion for distilling entanglement using the same class of (one-way) channels, yielding one of the few entanglement measures that is monotonic under local operations with one-way classical communication (1-LOCC), but not under the more general class of local operations with classical communication (LOCC).
Smith Graeme
Smolin John A.
Winter Andreas
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