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Science 25 February 2005:
Vol. 307. no. 5713, pp. 1299 - 1302
DOI: 10.1126/science.1107572
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Reports

Simultaneous State Measurement of Coupled Josephson Phase Qubits

R. McDermott,1,2 R. W. Simmonds,2 Matthias Steffen,1 K. B. Cooper,1 K. Cicak,2 K. D. Osborn,2 Seongshik Oh,2 D. P. Pappas,2 John M. Martinis1*

One of the many challenges of building a scalable quantum computer is single-shot measurement of all the quantum bits (qubits). We have used simultaneous single-shot measurement of coupled Josephson phase qubits to directly probe interaction of the qubits in the time domain. The concept of measurement crosstalk is introduced, and we show that its effects are minimized by careful adjustment of the timing of the measurements. We observe the antiphase oscillation of the two-qubit |01> and |10> states, consistent with quantum mechanical entanglement of these states, thereby opening the possibility for full characterization of multiqubit gates and elementary quantum algorithms.

1 Department of Physics, University of California, Santa Barbara, CA 93106, USA.
2 National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA.

* To whom correspondence should be addressed. E-mail: martinis{at}physics.ucsb.edu

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