Skip to main content

Thank you for visiting nature.com. 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.

Quantum oscillations in two coupled charge qubits

Nature volume 421, pages 823–826 (2003)Cite this article

Abstract

A practical quantum computer1, if built, would consist of a set of coupled two-level quantum systems (qubits). Among the variety of qubits implemented2, solid-state qubits are of particular interest because of their potential suitability for integrated devices. A variety of qubits based on Josephson junctions3,4 have been implemented5,6,7,8; these exploit the coherence of Cooper-pair tunnelling in the superconducting state5,6,7,8,9,10. Despite apparent progress in the implementation of individual solid-state qubits, there have been no experimental reports of multiple qubit gates—a basic requirement for building a real quantum computer. Here we demonstrate a Josephson circuit consisting of two coupled charge qubits. Using a pulse technique, we coherently mix quantum states and observe quantum oscillations, the spectrum of which reflects interaction between the qubits. Our results demonstrate the feasibility of coupling multiple solid-state qubits, and indicate the existence of entangled two-qubit states.

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

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it

$39.95

Learn more

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

Figure 1: Two capacitively coupled charge qubits.
Figure 2: Pulse operation of device.
Figure 3: Quantum oscillations in qubits.
Figure 4: EJ1 dependence of the spectrum components obtained by Fourier transform of the oscillations at the co-resonance.

References

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

    MATH  Google Scholar 

  2. Clark, R. G. (ed.) Experimental Implementation of Quantum Computation (Rinton, Princeton, 2001)

  3. Averin, D. V. Quantum computing and quantum measurement with mesoscopic Josephson junctions. Fortschr. Phys. 48, 1055–1074 (2000)

    Article  Google Scholar 

  4. Makhlin, Y., Schön, G. & Shnirman, A. Quantum state engineering with Josephson-junction devices. Rev. Mod. Phys. 73, 357–400 (2001)

    Article  ADS  Google Scholar 

  5. 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 

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

    Article  ADS  CAS  Google Scholar 

  7. 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 

  8. 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 

  9. Friedman, J. R., Patel, V., Chen, W., Toltygo, S. K. & Lukens, J. E. Quantum superposition of distinct macroscopic states. Nature 406, 43–46 (2000)

    Article  ADS  CAS  Google Scholar 

  10. Van der Wal, C. H. et al. Quantum superposition of macroscopic persistent-current states. Science 290, 773–777 (2000)

    Article  ADS  CAS  Google Scholar 

  11. Bouchiat, V., Vion, D., Joyez, P., Esteve, D. & Devoret, M. H. Quantum coherence with a single Cooper pair. Phys. Scripta T 76, 165–170 (1998)

    Article  ADS  Google Scholar 

  12. Flees, D. J., Han, S. & Lukens, J. E. Interband transitions and band gap measurements in Bloch transistors. Phys. Rev. Lett. 78, 4817–4820 (1997)

    Article  ADS  CAS  Google Scholar 

  13. Nakamura, Y., Chen, C. D. & Tsai, J. S. Spectroscopy of energy-level splitting between two macroscopic quantum states of charge coherently superposed by Josephson coupling. Phys. Rev. Lett. 79, 2328–2331 (1997)

    Article  ADS  CAS  Google Scholar 

  14. Esteve, D. in Single Charge Tunneling (eds Grabert, H. & Devoret, M. H.) 109–137 (Plenum, New York, 1992)

    Book  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. Bennett, C. H., Bernstein, H. J., Popescu, S. & Schumacher, B. Concentrating partial entanglement by local operations. Phys. Rev. A 53, 2046–2052 (1996)

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

We thank B. L. Altshuler, X. D. Hu, H. Im, S. Ishizaka, F. Nori, T. Sakamoto and J. Q. You for discussions. D.V.A. was supported by AFORS, and by NSA and ARDA under an ARO contract.

Author information

Authors and Affiliations

  1. The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, 351-0198, Japan

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

  2. NEC Fundamental Research Laboratories, Tsukuba, Ibaraki, 305-8501, Japan

    T. Yamamoto, Y. Nakamura & J. S. Tsai

  3. Department of Physics and Astronomy, SUNY Stony Brook, New York, 11794-3800, USA

    D. V. Averin

  4. Lebedev Physical Institute, 117924, Moscow, Russia

    Yu. A. Pashkin

Authors
  1. Yu. A. Pashkin
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. T. Yamamoto
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. O. Astafiev
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Y. Nakamura
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. D. V. Averin
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. J. S. Tsai
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to J. S. Tsai.

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

Pashkin, Y., Yamamoto, T., Astafiev, O. et al. Quantum oscillations in two coupled charge qubits. Nature 421, 823–826 (2003). https://doi.org/10.1038/nature01365

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature01365

This article is cited by

Comments

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.

Search

Advanced search

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