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Science 8 September 2006:
Vol. 313. no. 5792, pp. 1423 - 1425
DOI: 10.1126/science.1130886
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Reports

Measurement of the Entanglement of Two Superconducting Qubits via State Tomography

Matthias Steffen,* M. Ansmann, Radoslaw C. Bialczak, N. Katz, Erik Lucero, R. McDermott, Matthew Neeley, E. M. Weig, A. N. Cleland, John M. Martinis{dagger}

Demonstration of quantum entanglement, a key resource in quantum computation arising from a nonclassical correlation of states, requires complete measurement of all states in varying bases. By using simultaneous measurement and state tomography, we demonstrated entanglement between two solid-state qubits. Single qubit operations and capacitive coupling between two super-conducting phase qubits were used to generate a Bell-type state. Full two-qubit tomography yielded a density matrix showing an entangled state with fidelity up to 87%. Our results demonstrate a high degree of unitary control of the system, indicating that larger implementations are within reach.

Department of Physics and California Nano Systems Institute, University of California, Santa Barbara, CA 93106, USA.

* Present address: IBM Watson Research Center, Yorktown Heights, NY 10598, USA.

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

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Observation of Berry's Phase in a Solid-State Qubit.
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