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Published Online February 13, 2003
Science DOI: 10.1126/science.1081045

Reports

Submitted on December 2, 2002
Accepted on February 4, 2003

Coherent Quantum Dynamics of a Superconducting Flux Qubit

I. Chiorescu 1*, Y. Nakamura 2, C. J. P. M. Harmans 1, J. E. Mooij 1

1 Quantum Transport Group, Nano-Science Department, Delft University of Technology and Delft Institute for Micro Electronics and Submicron Technology (DIMES), Lorentzweg 1, 2628 CJ, Delft, Netherlands.
2 Quantum Transport Group, Nano-Science Department, Delft University of Technology and Delft Institute for Micro Electronics and Submicron Technology (DIMES), Lorentzweg 1, 2628 CJ, Delft, Netherlands; 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.

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.


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