title: Quantum oscillations in two coupled charge qubits.
abstract: A practical quantum computer, if built, would consist of a set of coupled two-level quantum systems (qubits). Among the variety of qubits implemented, solid-state qubits are of particular interest because of their potential suitability for integrated devices. A variety of qubits based on Josephson junctions have been implemented; these exploit the coherence of Cooper-pair tunnelling in the superconducting state. Despite apparent progress in the implementation of individual solid-state qubits, there have been no experimental reports of multiple qubit gates--a basic requirement for building a real quantum computer. Here we demonstrate a Josephson circuit consisting of two coupled charge qubits. Using a pulse technique, we coherently mix quantum states and observe quantum oscillations, the spectrum of which reflects interaction between the qubits. Our results demonstrate the feasibility of coupling multiple solid-state qubits, and indicate the existence of entangled two-qubit states.
authors.affiliation: The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan.
authors.forename: Yu A
authors.initials: YA
authors.lastname: Pashkin
authors.forename: T
authors.initials: T
authors.lastname: Yamamoto
authors.forename: O
authors.initials: O
authors.lastname: Astafiev
authors.forename: Y
authors.initials: Y
authors.lastname: Nakamura
authors.forename: D V
authors.initials: DV
authors.lastname: Averin
authors.forename: J S
authors.initials: JS
authors.lastname: Tsai