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Originally published in Science Express on 13 February 2003
Science 21 March 2003:
Vol. 299. no. 5614, pp. 1869 - 1871
DOI: 10.1126/science.1081045
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Reports

Coherent Quantum Dynamics of a Superconducting Flux Qubit

I. Chiorescu,1* Y. Nakamura,12 C. J. P. M. Harmans,1 J. E. Mooij1

We have observed coherent time evolution between two quantum states of a superconducting flux qubit comprising three Josephson junctions in a loop. The superposition of the two states carrying opposite macroscopic persistent currents is manipulated by resonant microwave pulses. Readout by means of switching-event measurement with an attached superconducting quantum interference device revealed quantum-state oscillations with high fidelity. Under strong microwave driving, it was possible to induce hundreds of coherent oscillations. Pulsed operations on this first sample yielded a relaxation time of 900 nanoseconds and a free-induction dephasing time of 20 nanoseconds. These results are promising for future solid-state quantum computing.

1 Quantum Transport Group, Department of NanoScience, Delft University of Technology and Delft Institute for Micro Electronics and Submicron Technology (DIMES), Lorentzweg 1, 2628 CJ Delft, Netherlands.
2 NEC Fundamental Research Laboratories, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan.
*   To whom correspondence should be addressed. E-mail: chiorescu{at}qt.tn.tudelft.nl

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