Phys. Rev. A 69, 010303 (2004) [4 pages]Transition behavior in the channel capacity of two-quibit channels with memory |
Chiara Macchiavello1, G. Massimo Palma2, and S. Virmani3
1Dipartimento di Fisica “A.Volta,” and Istituto Nazionale per la Fisica della Materia (INFM), Via Bassi 6, I-27100 Pavia, Italy
2INFM-NEST, Dipartimento di Tecnologie dell’Informazione, Università degli Studi di Milano, via Bramante 65, I-26013 Crema (CR), Italy
3QOLS, Department of Physics, Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BW, United KingdomDepartment of Computer Science, University of Hertfordshire, College Lane, Hatfield AL10 9AB, United Kingdom
Received 3 July 2003; published 15 January 2004
We prove that a general upper bound on the maximal mutual information of quantum channels is saturated in the case of Pauli channels with an arbitrary degree of memory. For a subset of such channels we explicitly identify the optimal signal states. We show analytically that for such a class of channels entangled states are indeed optimal above a given memory threshold.
©2004 The American Physical Society
URL: http://link.aps.org/abstract/PRA/v69/e010303
DOI: 10.1103/PhysRevA.69.010303
PACS: 03.67.Hk
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