Macroscopic Quantum Superposition in a Three-Josephson-Junction Loop

  • Caspar H. van der Wal
  • A. C. J. ter Haar
  • F. K. Wilhelm
  • R. N. Schouten
  • C. J. P. M. Harmans
  • T. P. Orlando
  • Seth Lloyd
  • J. E. Mooij
Chapter

Abstract

We present microwave-spectroscopy experiments on two quantum levels of a superconducting loop with three Josephson junctions. The level separation between the ground state and first excited state shows an anti-crossing where two classical persistent-current states with opposite polarity are degenerate. This is evidence for symmetric and antisymmetric quantum superpositions of two macroscopic states; the classical states have persistent currents of 0.5 µA and correspond to the center-of-mass motion of millions of Cooper pairs. A study of the thermal occupancies of the two quantum levels shows that the loop is at low temperatures in a non-equilibrium state.

Keywords

Macroscopic quantum mechanics Josephson effect SQUIDs microwave spectroscopy 
This is a preview of subscription content, log in to check access.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. [1]
    P. W. Anderson, in Lectures on the Many-Body Problem, E. R. Caianiello, Ed. (Academic Press, New York, 1964), vol. 2, pp. 113–135.CrossRefGoogle Scholar
  2. [2]
    A. J. Leggett, Prog. Theor. Phys. Suppl. 69, 80 (1980).MathSciNetADSCrossRefGoogle Scholar
  3. [3]
    K. K. Likharev, Sov. Phys. Usp. 26, 87 (1983).ADSCrossRefGoogle Scholar
  4. [4]
    W. H. Zurek, Phys. Today 44, 36 (October 1991).CrossRefGoogle Scholar
  5. [5]
    A. J. Leggett, A. Garg, Phys. Rev. Lett. 54, 857 (1985).MathSciNetADSCrossRefGoogle Scholar
  6. [6]
    M. F. Bocko et al., IEEE Trans. Appl. Supercond. 7, 3638 (1997).CrossRefGoogle Scholar
  7. [7]
    L. B. loffe et al., Nature 398, 679 (1999).ADSCrossRefGoogle Scholar
  8. [8]
    J. E. Mooij et al., Science 285, 1036 (1999).CrossRefGoogle Scholar
  9. [9]
    T. P. Orlando et al., Phys. Rev. B. 60, 15398 (1999).ADSCrossRefGoogle Scholar
  10. [10]
    [10] We acknowledge that the results presented here do not exclude alternative theories for quantum mechanics (e. g. macro-realistic theories). This would require a type of experiment as proposed by Leggett et al. [5].Google Scholar
  11. [11]
    [11] C. H. van der Wal et al., submitted to Science.Google Scholar
  12. [12]
    J. R. Friedman et al., Nature 406, 43 (2000).ADSCrossRefGoogle Scholar
  13. [13]
    R. Rouse, S. Han, J. E. Lukens, Phys. Rev. Lett. 75, 1614 (1995).ADSCrossRefGoogle Scholar
  14. [14]
    C. Cosmelli et al., Phys. Rev. Lett. 82, 5357 (1999).ADSCrossRefGoogle Scholar
  15. [15]
    S. Han, R. Rouse, J. E. Lukens, Phys. Rev. Lett. 84, 1300 (2000).ADSCrossRefGoogle Scholar
  16. [16]
    W. Wernsdorfer, R. Sessoli, Science 284, 133 (1999).ADSCrossRefGoogle Scholar
  17. [17]
    M. Arndt et al., Nature 401, 680 (1999).ADSCrossRefGoogle Scholar
  18. [18]
    T. H. Oosterkamp et al., Nature 395, 873 (1998).ADSCrossRefGoogle Scholar
  19. [19]
    Y. Nakamura et al., Phys. Rev. Lett. 79, 2328 (1997).ADSCrossRefGoogle Scholar
  20. [20]
    V. Bouchiat et al., Phys. Scr. T76, 165 (1998).ADSCrossRefGoogle Scholar
  21. [21]
    D. J. Flees, S. Han, J. E. Lukens, J. Supercond. 12, 813 (1999).ADSCrossRefGoogle Scholar
  22. [22]
    Y. Nakamura, Yu. A. Pashkin, J. S. Tsai, Nature 398, 786 (1999).ADSCrossRefGoogle Scholar
  23. [23]
    C. H. van der Wal, J. E. Mooij, J. Supercond. 12, 807 (1999).ADSCrossRefGoogle Scholar
  24. [24]
    A. J. Leggett et al., Rev. Mod. Phys. 59, 1 (1987).ADSCrossRefGoogle Scholar
  25. [25]
    N. Prokof’ev, P. Stamp, Rep. Prog. Phys. 63, 669 (2000).ADSCrossRefGoogle Scholar
  26. [26]
    L. Tian et al., to be published; cond-mat/9910062.Google Scholar
  27. [27]
    P. Silvestrini et al., Phys. Rev. Lett. 79, 3046 (1997).ADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2001

Authors and Affiliations

  • Caspar H. van der Wal
    • 1
  • A. C. J. ter Haar
    • 1
  • F. K. Wilhelm
    • 1
  • R. N. Schouten
    • 1
  • C. J. P. M. Harmans
    • 1
  • T. P. Orlando
    • 2
  • Seth Lloyd
    • 3
  • J. E. Mooij
    • 1
    • 2
  1. 1.Department of Applied Physics and Delft Institute for Micro Electronics and Submicron Technology (DIMES)Delft University of TechnologyDelftthe Netherlands
  2. 2.Department of Electrical Engineering and Computer ScienceMITCambridgeUSA
  3. 3.Department of Mechanical EngineeringMITCambridgeUSA

Personalised recommendations