title: Quantum circuits for general multiqubit gates.
abstract: We consider a generic elementary gate sequence which is needed to implement a general quantum gate acting on n qubits-a unitary transformation with 4(n) degrees of freedom. For synthesizing the gate sequence, a method based on the so-called cosine-sine matrix decomposition is presented. The result is optimal in the number of elementary one-qubit gates, 4(n), and scales more favorably than the previously reported decompositions requiring 4(n)-2(n+1) controlled NOT gates.
authors.affiliation: Materials Physics Laboratory, POB 2200 (Technical Physics), FIN-02015 HUT, Helsinki University of Technology, Finland. mpmotton@focus.hut.fi
authors.forename: Mikko
authors.initials: M
authors.lastname: Möttönen
authors.forename: Juha J
authors.initials: JJ
authors.lastname: Vartiainen
authors.forename: Ville
authors.initials: V
authors.lastname: Bergholm
authors.forename: Martti M
authors.initials: MM
authors.lastname: Salomaa