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Coupling superconducting qubits via a cavity bus

Abstract

Superconducting circuits are promising candidates for constructing quantum bits (qubits) in a quantum computer; single-qubit operations are now routine1,2, and several examples3,4,5,6,7,8,9 of two-qubit interactions and gates have been demonstrated. These experiments show that two nearby qubits can be readily coupled with local interactions. Performing gate operations between an arbitrary pair of distant qubits is highly desirable for any quantum computer architecture, but has not yet been demonstrated. An efficient way to achieve this goal is to couple the qubits to a ‘quantum bus’, which distributes quantum information among the qubits. Here we show the implementation of such a quantum bus, using microwave photons confined in a transmission line cavity, to couple two superconducting qubits on opposite sides of a chip. The interaction is mediated by the exchange of virtual rather than real photons, avoiding cavity-induced loss. Using fast control of the qubits to switch the coupling effectively on and off, we demonstrate coherent transfer of quantum states between the qubits. The cavity is also used to perform multiplexed control and measurement of the qubit states. This approach can be expanded to more than two qubits, and is an attractive architecture for quantum information processing on a chip.

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Figure 1: Sample and scheme used to couple two qubits to an on-chip microwave cavity.
Figure 2: Cavity transmission and spectroscopy of single and coupled qubits.
Figure 3: Multiplexed control and read-out of uncoupled qubits.
Figure 4: Controllable effective coupling and coherent state transfer via off-resonant Stark shift.

References

  1. Devoret, M. H. & Martinis, J. M. Implementing qubits with superconducting integrated circuits. Quantum Inform. Process. 3, 163–203 (2004)

    Article  Google Scholar 

  2. You, J. Q. & Nori, F. Superconducting circuits and quantum information. Phys. Today 58, 42–47 (2005)

    Article  CAS  Google Scholar 

  3. Yamamoto, T., Pashkin, Y. A., Astafiev, O., Nakamura, Y. & Tsai, J. S. Demonstration of conditional gate operation using superconducting charge qubits. Nature 425, 941–944 (2003)

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  5. Majer, J. B., Paauw, F. G., ter Haar, A. C. J., Harmans, C. J. P. M. & Mooij, J. E. Spectroscopy on two coupled superconducting flux qubits. Phys. Rev. Lett. 94, 090501 (2005)

    Article  ADS  CAS  Google Scholar 

  6. Steffen, M. et al. Measurement of the entanglement of two superconducting qubits via state tomography. Science 313, 1423–1425 (2006)

    Article  ADS  MathSciNet  CAS  Google Scholar 

  7. Hime, T. et al. Solid-state qubits with current-controlled coupling. Science 314, 1427–1429 (2006)

    Article  ADS  CAS  Google Scholar 

  8. van der Ploeg, S. H. W. et al. Controllable coupling of superconducting flux qubits. Phys. Rev. Lett. 98, 057004 (2007)

    Article  ADS  CAS  Google Scholar 

  9. Niskanen, A. O. et al. Quantum coherent tunable coupling of superconducting qubits. Science 316, 723–726 (2007)

    Article  ADS  CAS  Google Scholar 

  10. Cirac, J. I. & Zoller, P. Quantum computations with cold trapped ions. Phys. Rev. Lett. 74, 4091–4094 (1995)

    Article  ADS  CAS  Google Scholar 

  11. Leibfried, D., Blatt, R., Monroe, C. & Wineland, D. Quantum dynamics of single trapped ions. Rev. Mod. Phys. 75, 281–324 (2003)

    Article  ADS  CAS  Google Scholar 

  12. Duan, L. M., Lukin, M. D., Cirac, J. I. & Zoller, P. Long-distance quantum communication with atomic ensembles and linear optics. Nature 414, 413–418 (2001)

    Article  ADS  CAS  Google Scholar 

  13. Chou, C.-W. et al. Functional quantum nodes for entanglement distribution over scalable quantum networks. Science 316, 1316–1320 (2007)

    Article  ADS  CAS  Google Scholar 

  14. Mabuchi, H. & Doherty, A. C. Cavity quantum electrodynamics: coherence in context. Science 298, 1372–1377 (2002)

    Article  ADS  CAS  Google Scholar 

  15. Hagley, E. et al. Generation of Einstein-Podolsky-Rosen pairs of atoms. Phys. Rev. Lett. 79, 1–5 (1997)

    Article  ADS  CAS  Google Scholar 

  16. Zheng, S.-B. & Guo, G.-C. Efficient scheme for two-atom entanglement and quantum information processing in cavity QED. Phys. Rev. Lett. 85, 2392–2395 (2000)

    Article  ADS  CAS  Google Scholar 

  17. Osnaghi, S. et al. Coherent control of an atomic collision in a cavity. Phys. Rev. Lett. 87, 037902 (2001)

    Article  ADS  CAS  Google Scholar 

  18. Blais, A., Huang, R.-S., Wallraff, A., Girvin, S. M. & Schoelkopf, R. J. Cavity quantum electrodynamics for superconducting electrical circuits: an architecture for quantum computation. Phys. Rev. A. 69, 062320 (2004)

    Article  ADS  Google Scholar 

  19. Wallraff, A. et al. Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics. Nature 431, 162–167 (2004)

    Article  ADS  CAS  Google Scholar 

  20. Houck, A. A. et al. Generating single microwave photons in a circuit. Nature 449, 328–331 (2007)

    Article  ADS  CAS  Google Scholar 

  21. Koch, J. et al. Charge insensitive qubit design derived from the Cooper Pair Box. Phys. Rev. A (in the press); preprint at 〈http://arxiv.org/abs/cond-mat/0703002〉 (2007)

  22. Blais, A. et al. Quantum-information processing with circuit quantum electrodynamics. Phys. Rev. A. 75, 032329 (2007)

    Article  ADS  Google Scholar 

  23. Schuster, D. I. et al. ac Stark shift and dephasing of a superconducting qubit strongly coupled to a cavity field. Phys. Rev. Lett. 94, 123602 (2005)

    Article  ADS  CAS  Google Scholar 

  24. Gershenfeld, N. A. & Chuang, I. L. Bulk spin-resonance quantum computation. Science 275, 350–356 (1997)

    Article  MathSciNet  CAS  Google Scholar 

  25. Schuster, D. I. et al. Resolving photon number states in a superconducting circuit. Nature 445, 515–518 (2007)

    Article  ADS  CAS  Google Scholar 

  26. Grangier, P., Aspect, A. & Vigue, J. Quantum interference effect for two atoms radiating a single photon. Phys. Rev. Lett. 54, 418–421 (1985)

    Article  ADS  CAS  Google Scholar 

  27. Itano, W. M. et al. Complementarity and Young’s interference fringes from two atoms. Phys. Rev. A. 57, 4176–4187 (1998)

    Article  ADS  CAS  Google Scholar 

  28. Wallraff, A. et al. Approaching unit visibility for control of a superconducting qubit with dispersive readout. Phys. Rev. Lett. 95, 060501 (2005)

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

This work was supported in part by the National Security Agency under the Army Research Office, by the NSF, and by Yale University. J.M.C. acknowledges support from an NSF Graduate Research Fellowship. J.K. and A.A.H. acknowledge support from Yale University via a Quantum Information and Mesoscopic Physics Fellowship. L.F. acknowledges partial support from the CNR-Istituto di Cibernetica, Pozzuoli, Italy. A.B. was supported by NSERC, CIAR and FQRNT.

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Correspondence to J. Majer or R. J. Schoelkopf.

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Majer, J., Chow, J., Gambetta, J. et al. Coupling superconducting qubits via a cavity bus. Nature 449, 443–447 (2007). https://doi.org/10.1038/nature06184

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