title: Classical capacity of quantum thermal noise channels to within 1.45 bits.
abstract: We find a tight upper bound for the classical capacity of quantum thermal noise channels that is within 1/ln2 bits of Holevo's lower bound. This lower bound is achievable using unentangled, classical signal states, namely, displaced coherent states. Thus, we find that while quantum tricks might offer benefits, when it comes to classical communication, they can only help a bit.
authors.affiliation: IBM Thomas J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, USA and Institute for Quantum Computing, University of Waterloo, 200 University Avenue West Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: König
authors.affiliation: IBM Thomas J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598, USA.
authors.forename: Graeme
authors.initials: G
authors.lastname: Smith