title: Limitations on practical quantum cryptography
abstract: We provide limits to practical quantum key distribution, taking into account channel losses, a realistic detection process, and imperfections in the "qubits" sent from the sender to the receiver. As we show, even quantum key distribution with perfect qubits might not be achievable over long distances when the other imperfections are taken into account. Furthermore, existing experimental schemes (based on weak pulses) currently do not offer unconditional security for the reported distances and signal strength. Finally we show that parametric down-conversion offers enhanced performance compared to its weak coherent pulse counterpart.
authors.affiliation: Departement IRO, Universite de Montreal, C.P. 6128, succursale centre-ville, Montreal, Quebec Canada H3C 3J7.
authors.initials: G
authors.lastname: Brassard
authors.initials: N
authors.lastname: Lutkenhaus
authors.initials: T
authors.lastname: Mor
authors.initials: BC
authors.lastname: Sanders