Letter | Published:

Single-shot qubit readout in circuit quantum electrodynamics

Nature Physics volume 5, pages 791795 (2009) | Download Citation



The future development of quantum information using superconducting circuits requires Josephson qubits1 with long coherence times combined with a high-fidelity readout. Significant progress in the control of coherence has recently been achieved using circuit quantum electrodynamics architectures2,3, where the qubit is embedded in a coplanar waveguide resonator, which both provides a well-controlled electromagnetic environment and serves as qubit readout. In particular, a new qubit design, the so-called transmon, yields reproducibly long coherence times4,5. However, a high-fidelity single-shot readout of the transmon, desirable for running simple quantum algorithms or measuring quantum correlations in multi-qubit experiments, is still lacking. Here, we demonstrate a new transmon circuit where the waveguide resonator is turned into a sample-and-hold detector—more specifically, a Josephson bifurcation amplifier6,7—which allows both fast measurement and single-shot discrimination of the qubit states. We report Rabi oscillations with a high visibility of 94%, together with dephasing and relaxation times longer than 0.5 μs. By carrying out two measurements in series, we also demonstrate that this new readout does not induce extra qubit relaxation.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    & in Superconducting Quantum Circuits, Qubits and Computing (eds Rieth, M. & Schommers, W.) (Handbook of Theoretical and Computational Nanotechnology, Vol. 3, American Scientific, 2006).

  2. 2.

    , , , & Cavity quantum electrodynamics for superconducting electrical circuits: An architecture for quantum computation. Phys. Rev. A 69, 062320 (2004).

  3. 3.

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

  4. 4.

    et al. Charge-insensitive qubit design derived from the Cooper pair box. Phys. Rev. A 76, 042319 (2007).

  5. 5.

    et al. Suppressing charge noise decoherence in superconducting charge qubits. Phys. Rev. B 77, 180502 (2008).

  6. 6.

    et al. RF-driven Josephson bifurcation amplifier for quantum measurement. Phys. Rev. Lett. 93, 207002 (2004).

  7. 7.

    et al. Dispersive microwave bifurcation of a superconducting resonator cavity incorporating a Josephson junction. Preprint at <> (2007).

  8. 8.

    , & Nonlinear dispersive regime of cavity QED: The dressed dephasing model. Phys. Rev. A 77, 060305 (2008).

  9. 9.

    et al. High-fidelity gates in a single Josephson qubit. Phys. Rev. Lett. 100, 247001 (2008).

  10. 10.

    , , & Rabi oscillations in a large Josephson-junction qubit. Phys. Rev. Lett. 89, 117901 (2002).

  11. 11.

    et al. Dispersive measurements of superconducting qubit coherence with a fast latching readout. Phys. Rev. B 73, 054510 (2006).

  12. 12.

    et al. Quantum nondemolition readout using a Josephson bifurcation amplifier. Phys. Rev. B 76, 014525 (2007).

  13. 13.

    et al. Measuring the decoherence of a quantronium qubit with the cavity bifurcation amplifier. Phys. Rev. B 76, 174516 (2007).

  14. 14.

    , , , & High-contrast dispersive readout of a superconducting flux qubit using a nonlinear resonator. Phys. Rev. Lett. 96, 127003 (2006).

  15. 15.

    et al. Quantum non-demolition measurement of a superconducting two-level system. Nature Phys. 3, 119–125 (2007).

  16. 16.

    et al. Ac stark shift and dephasing of a superconducting qubit strongly coupled to a cavity field. Phys. Rev. Lett. 94, 123602 (2004).

  17. 17.

    & Fluctuations in nonlinear systems near bifurcations corresponding to the appearance of new stable states. Physica A 104, 480–494 (1980).

  18. 18.

    PhD thesis (2008), available online at <>.

  19. 19.

    , , , & Role of relaxation in the quantum measurement of a superconducting qubit using a nonlinear oscillator. Phys. Rev. B 78, 132508 (2008).

  20. 20.

    et al. Controlling the spontaneous emission of a superconducting transmon qubit. Phys. Rev. Lett. 101, 080502 (2008).

  21. 21.

    , & Effect of an arbitrary dissipative circuit on the quantum energy levels and tunneling of a Josephson junction. Phys. Rev. B 34, 158–163 (1986).

  22. 22.

    et al. Decoherence in a superconducting quantum bit circuit. Phys. Rev. B 72, 134519 (2005).

  23. 23.

    et al. Low-frequency noise in dc superconducting quantum interference devices below 1 K. Appl. Phys. Lett. 50, 772–774 (1987).

  24. 24.

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

Download references


We acknowledge financial support from European projects EuroSQIP and Midas, from ANR-08-BLAN-0074-01 and from Region Ile-de-France for the nanofabrication facility at SPEC. We gratefully thank P. Senat and P. Orfila for technical support, and acknowledge useful discussions within the Quantronics group and with A. Lupascu, I. Siddiqi, M. Devoret, A. Wallraff and A. Blais.

Author information


  1. Quantronics group, Service de Physique de l’État Condensé (CNRS URA 2464), DSM/IRAMIS/SPEC, CEA-Saclay, 91191 Gif-sur-Yvette cedex, France

    • François Mallet
    • , Florian R. Ong
    • , Agustin Palacios-Laloy
    • , François Nguyen
    • , Patrice Bertet
    • , Denis Vion
    •  & Daniel Esteve


  1. Search for François Mallet in:

  2. Search for Florian R. Ong in:

  3. Search for Agustin Palacios-Laloy in:

  4. Search for François Nguyen in:

  5. Search for Patrice Bertet in:

  6. Search for Denis Vion in:

  7. Search for Daniel Esteve in:


F.M., P.B., D.V. and D.E. designed the experiment, F.R.O. fabricated the sample, F.M., F.N., A.P.-L., F.R.O. and P.B. carried out the measurements, and all of the authors contributed to the writing of the manuscript.

Corresponding author

Correspondence to Denis Vion.

About this article

Publication history






Further reading