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Published Online May 15, 2003
Science DOI: 10.1126/science.1084528

Reports

Submitted on March 13, 2003
Accepted on April 30, 2003

Entangled Macroscopic Quantum States in Two Superconducting Qubits

A. J. Berkley 1*, H. Xu 1, R. C. Ramos 1, M. A. Gubrud 1, F. W. Strauch 1, P. R. Johnson 1, J. R. Anderson 1, A. J. Dragt 1, C. J. Lobb 1, F. C. Wellstood 1

1 Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20742, USA.

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

We present spectroscopic evidence for the creation of entangled macroscopic quantum states in two current-biased Josephson-junction qubits coupled by a capacitor. The individual junction bias currents are used to control the interaction between the qubits by tuning the energy level spacings of the junctions in and out of resonance with each other. Microwave spectroscopy in the 4-6 GHz range at 20 mK reveals energy levels which agree well with theoretical results for entangled states. The single qubits are spatially separate and the entangled states extend over the 0.7 mm distance between the two qubits.


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