title: Decoherence of an n-qubit quantum memory.
abstract: We analyze decoherence of a quantum register in the absence of nonlocal operations, i.e., n noninteracting qubits coupled to an environment. The problem is solved in terms of a sum rule which implies linear scaling in the number of qubits. Each term involves a single qubit and its entanglement with the remaining ones. Two conditions are essential: first, decoherence must be small, and second, the coupling of different qubits must be uncorrelated in the interaction picture. We apply the result to a random matrix model, and illustrate its reach considering a Greenberger-Horne-Zeilinger state coupled to a spin bath.
authors.affiliation: Departamento de Física, Universidad de Guadalajara, Guadalajara, México.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gorin
authors.forename: Carlos
authors.initials: C
authors.lastname: Pineda
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Seligman