Unbounded number of channel uses are required to see quantum capacity



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Cubitt, Toby S. and Elkouss Coronas, David and Matthews, William and Ozols, M. and Pérez García, David and Strelchuk, S. (2015) Unbounded number of channel uses are required to see quantum capacity. Nature communications, 6 . ISSN 2041-1723

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Official URL: http://www.nature.com/ncomms/2015/150331/ncomms7739/full/ncomms7739.html


Transmitting data reliably over noisy communication channels is one of the most important applications of information theory, and is well understood for channels modelled by classical physics. However, when quantum effects are involved, we do not know how to compute channel capacities. This is because the formula for the quantum capacity involves maximizing the coherent information over an unbounded number of channel uses. In fact, entanglement across channel uses can even increase the coherent information from zero to non-zero. Here we study the number of channel uses necessary to detect positive coherent information. In all previous known examples, two channel uses already sufficed. It might be that only a finite number of channel uses is always sufficient. We show that this is not the case: for any number of uses, there are channels for which the coherent information is zero, but which nonetheless have capacity

Item Type:Article
Uncontrolled Keywords:Physical sciences, Theoretical physics
Subjects:Sciences > Mathematics
ID Code:30127
Deposited On:18 May 2015 08:31
Last Modified:12 Dec 2018 15:06

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