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Science 1 December 2006:
Vol. 314. no. 5804, pp. 1427 - 1429
DOI: 10.1126/science.1134388
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Reports

Solid-State Qubits with Current-Controlled Coupling

T. Hime,1 P. A. Reichardt,1 B. L. T. Plourde,1,2 T. L. Robertson,1* C.-E. Wu,1{dagger} A. V. Ustinov,1{ddagger} John Clarke1§

The ability to switch the coupling between quantum bits (qubits) on and off is essential for implementing many quantum-computing algorithms. We demonstrated such control with two flux qubits coupled together through their mutual inductances and through the dc superconducting quantum interference device (SQUID) that reads out their magnetic flux states. A bias current applied to the SQUID in the zero-voltage state induced a change in the dynamic inductance, reducing the coupling energy controllably to zero and reversing its sign.

1 Department of Physics, University of California, Berkeley, CA 94720–7300, USA.
2 Department of Physics, Syracuse University, Syracuse, NY 13244–1130, USA.

Note added in proof: S. H. W. van der Ploeg et al. (preprint available at http://arxiv.org/abs/cond-mat/0605588) reported two flux qubits in which the coupling was controlled by means of a coupler loop and demonstrated that the sign of the ground state could be changed from antiferromagnetic to ferromagnetic. Spectroscopy of excited states was not described.

* Present address: Proteus Biomedical, 750 Chesapeake Drive, Redwood City, CA 94063, USA.

{dagger} Present address: Department of Physics, National Tsinghua University, Hsinchu 300, Taiwan.

{ddagger} Permanent address: Physikalisches Institut III, Universität Erlangen-Nürnberg, Erwin-Rommel-Strasse 1, D-91058 Erlangen, Germany.

§ To whom correspondence should be addressed. E-mail: jclarke{at}berkeley.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Quantum Coherent Tunable Coupling of Superconducting Qubits.
A. O. Niskanen, K. Harrabi, F. Yoshihara, Y. Nakamura, S. Lloyd, and J. S. Tsai (2007)
Science 316, 723-726
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