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Published Online August 21, 2008
Science DOI: 10.1126/science.1162242

Reports

Submitted on June 24, 2008
Accepted on August 13, 2008

Quantum Communication with Zero-Capacity Channels

Graeme Smith 1* and Jon Yard 2

1 IBM T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598, USA.
2 Quantum Institute, Center for Nonlinear Studies (CNLS), Computer, Computational and Statistical Sciences (CCS-3), Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

* To whom correspondence should be addressed.
Graeme Smith , E-mail: gsbsmith{at}gmail.com

Communication over a noisy quantum channel introduces errors in the transmission that must be corrected. A fundamental bound on quantum error correction is the quantum capacity, which quantifies the amount of quantum data that can be protected. We show theoretically that two quantum channels, each with a transmission capacity of zero, can have a nonzero capacity when used together. This unveils a rich structure in the theory of quantum communications, implying that the quantum capacity does not uniquely specify a channel's ability for transmitting quantum information.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)