Quantum Theory and Classical Information

Göran Einarsson

Published 2002-02-21, updated 2002-09-03Version 2

Transmission of classical information using quantum objects such as polarized photons is studied. The classical (Shannon) channel capacity and its relation to quantum (von Neumann) channel capacity is investigated for various receiver arrangements. A quantum channel with transmission impairment caused by attenuation and random polarization noise is considered. It is shown that the maximal (von Neumann) capacity of such a channel can be realized by a simple symbol by symbol detector followed by a classical error correcting decoder. For an intensity limited optical channel capacity is achieved by on-off keying (OOK). The capacity per unit cost is shown to be 1 nat/photon = 1.44 bit/photon, slightly larger than the 1 bit/photon obtained by orthogonal quantum signals.