Broadcast of classical information through a quantum channel
Yerevan Physics Institute -
Alikhanian Brothers St. 2, Yerevan 375036, Armenia
2 Institute of Theoretical Physics, University of Amsterdam Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
Accepted: 19 April 2000
We consider transmission of classical information through a quantum channel from one sender to several receivers. In contrast to quantum information, classical information carried by two non-orthogonal states of a quantum system can be cloned exactly. This restricts a naive extrapolation of the standard no-cloning theorem. The optimal cloning induces entanglement between clones which increases with non-orthogonality of the states. The capacity of the corresponding quantum channel is considered. As a byproduct of our results, we obtain that for an entangled system with an unknown state there is no transformation which removes the entanglement totally without affecting the corresponding marginal density matrices.
PACS: 03.65.Bz – Quantum mechanics: Foundations, theory of measurement, miscellaneous theories (including Aharonov-Bohm effect, Bell inequalities, Berry's phase) / 03.67.-a – Quantum information / 03.67.Hk – Quantum communication
© EDP Sciences, 2000