title: Substituting a qubit for an arbitrarily large number of classical bits.
abstract: We show that a qubit can be used to substitute for a classical analog system requiring an arbitrarily large number of classical bits to represent digitally. Let a physical system S interact locally with a classical field varphi(x) as S travels directly from point A to point B. Our task is to use S to answer a simple yes/no question about varphi(x). If S is a qubit, the task can be done perfectly. We show that any classical system S must encode an arbitrarily large number of classical bits to solve the same task. This result implies a large quantum advantage in the memory size necessary for some computations. We also show that no finite amount of one-way classical communication can perfectly simulate the effect of quantum entanglement.
authors.affiliation: Perimeter Institute for Theoretical Physics, 35 King Street North, Waterloo, Ontario, Canada N2J 2W9.
authors.forename: Ernesto F
authors.initials: EF
authors.lastname: Galvão
authors.forename: Lucien
authors.initials: L
authors.lastname: Hardy