Coupled Josephson quantum bits

J. S. Tsai, T. Yamamoto, Yu A. Pashkin, O. Astafiev, Y. Nakamura

Research output: Contribution to journalConference articlepeer-review


The technologies of Josephson-junction-based qubits have been progressing rapidly, ever since its first demonstration by a superconducting charge qubit1. A variety of systems have been implemented2-5 with remarkable progress in coherence time and read-out schemes. Although the current level of this solid-state device is still not as advanced as that of the most advanced microscopic-system-based qubits6,7, these developments, together with the potential scalability, have renewed its position as a strong candidate as a building block for the quantum computer8. Recently, coherent oscillation9 and microwave spectroscopy 10 in capacitively-coupled superconducting qubits have been reported. The next challenging step toward quantum computation is a realization of logic gates11,12. Here we demonstrate a conditional gate operation using a pair of coupled superconducting charge qubits13. Using a pulse technique, we prepare different input states and show that they can be transformed by controlled-NOT (C-NOT) gate operation in the amplitude of the states. Although the phase evolution during the gate operation is still to be clarified, the present results are a major step toward the realization of a universal solid-state quantum gate.

Original languageEnglish
Pages (from-to)11-18
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
Publication statusPublished - 2004
Externally publishedYes
EventNoise and Information in Nanoelectronics, Sensors, and Standards II - Maspalomas
Duration: 26 May 200428 May 2004


  • Josephson qubit


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