Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Demonstration of conditional gate operation using superconducting charge qubits


Following the demonstration of coherent control of the quantum state of a superconducting charge qubit1, a variety of qubits based on Josephson junctions have been implemented2,3,4,5. Although such solid-state devices are not currently as advanced as microscopic qubits based on nuclear magnetic resonance6 and ion trap7 technologies, the potential scalability of the former systems—together with progress in their coherence times and read-out schemes—makes them strong candidates for the building block of a quantum computer8. Recently, coherent oscillations9 and microwave spectroscopy10 of capacitively coupled superconducting qubits have been reported; the next challenging step towards quantum computation is the realization of logic gates11,12. Here we demonstrate conditional gate operation using a pair of coupled superconducting charge qubits. Using a pulse technique, we prepare different input states and show that their amplitude can be transformed by controlled-NOT (C-NOT) gate operation, although the phase evolution during the gate operation remains to be clarified.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Pulse operation of the coupled-qubit device.
Figure 2: Magnetic-flux dependence of the current of the control (top) and target (bottom) qubits under the application of pulses shown in Fig. 1c (i).
Figure 3: Pulse-induced current as a function of the Josephson energy of the control qubit.
Figure 4: Truth table of the present C-NOT operation estimated by the numerical calculation (solid blue bars).

Similar content being viewed by others


  1. Nakamura, Y., Pashkin, Yu. A. & Tsai, J. S. Coherent control of macroscopic quantum states in a single-Cooper-pair box. Nature 398, 786–788 (1999)

    Article  ADS  CAS  Google Scholar 

  2. Vion, D. et al. Manipulating the quantum state of an electrical circuit. Science 296, 886–889 (2002)

    Article  ADS  CAS  Google Scholar 

  3. Yu, Y., Han, S., Chu, X., Chu, S.-I. & Wang, Z. Coherent temporal oscillations of macroscopic quantum states in a Josephson junction. Science 296, 889–892 (2002)

    Article  ADS  CAS  Google Scholar 

  4. Martinis, J. M., Nam, S., Aumentado, J. & Urbina, C. Rabi oscillations in a large Josephson-junction qubit. Phys. Rev. Lett. 89, 117901 (2002)

    Article  ADS  Google Scholar 

  5. Chiorescu, I., Nakamura, Y., Harmans, C. J. P. M. & Mooij, J. E. Coherent quantum dynamics of a superconducting flux qubit. Science 299, 1869–1871 (2003)

    Article  ADS  CAS  Google Scholar 

  6. Vandersypen, L. M. K. et al. Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance. Nature 414, 883–887 (2001)

    Article  ADS  CAS  Google Scholar 

  7. Gulde, S. et al. Implementation of the Deutsch-Jozsa algorithm on an ion-trap quantum computer. Nature 421, 48–50 (2003)

    Article  ADS  CAS  Google Scholar 

  8. Nielsen, M. A. & Chuang, I. L. Quantum Computation and Quantum Information (Cambridge Univ. Press, Cambridge, UK, 2000)

    MATH  Google Scholar 

  9. Pashkin, Yu. A. et al. Quantum oscillations in two coupled charge qubits. Nature 421, 823–826 (2003)

    Article  ADS  CAS  Google Scholar 

  10. Berkley, A. J. et al. Entangled macroscopic quantum states in two superconducting qubits. Science 300, 1548–1550 (2003)

    Article  ADS  CAS  Google Scholar 

  11. Shnirman, A., Schön, G. & Hermon, Z. Quantum manipulations of small Josephson junctions. Phys. Rev. Lett. 79, 2371–2374 (1997)

    Article  ADS  CAS  Google Scholar 

  12. Averin, D. V. Adiabatic quantum computation with Cooper pairs. Solid State Commun. 105, 659–664 (1998)

    Article  ADS  CAS  Google Scholar 

  13. Bouchiat, V., Vion, D., Joyez, P., Esteve, D. & Devoret, M. H. Quantum coherence with a single Cooper pair. Phys. Scripta T76, 165–170 (1998)

    Article  ADS  CAS  Google Scholar 

  14. Pothier, H., Lafarge, P., Urbina, C., Esteve, D. & Devoret, M. H. Single-electron pump based on charging effects. Europhys. Lett. 17, 249–254 (1992)

    Article  ADS  Google Scholar 

  15. Fulton, T. A., Gammel, P. L., Bishop, D. J., Dunkleberger, L. N. & Dolan, G. J. Observation of combined Josephson and charging effects in small tunnel junction circuits. Phys. Rev. Lett. 63, 1307–1310 (1989)

    Article  ADS  CAS  Google Scholar 

  16. Nakamura, Y., Pashkin, Yu. A., Yamamoto, T. & Tsai, J. S. Charge echo in a Cooper-pair box. Phys. Rev. Lett. 88, 047901 (2002)

    Article  ADS  CAS  Google Scholar 

Download references


We thank B. L. Altshuler, D. V. Averin, S. Ishizaka, F. Nori, T. Tilma, C. Urbina and J. Q. You for discussions.

Author information

Authors and Affiliations


Corresponding author

Correspondence to T. Yamamoto.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Yamamoto, T., Pashkin, Y., Astafiev, O. et al. Demonstration of conditional gate operation using superconducting charge qubits. Nature 425, 941–944 (2003).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing