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.

Probing the quantum vacuum with an artificial atom in front of a mirror


Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons, they still have a very real impact, for instance, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a superconducting circuit analogue of a mirror, creating regions in space where they are suppressed. Moving an artificial atom through these regions and measuring the spontaneous emission lifetime of the atom provides us with the spectral density of the vacuum fluctuations. Using the paradigm of waveguide quantum electrodynamics, we significantly improve over previous studies of the interaction of an atom with its mirror image, observing a spectral density as low as 0.02 quanta, a factor of 50 below the mirrorless result. This demonstrates that we can hide the atom from the vacuum, even though it is exposed in free space.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: An artificial atom in front of a mirror.
Figure 2: Spectroscopic measurements of the excited-state lifetime.
Figure 3: Calibrating the atom–field coupling.
Figure 4: The measured spectral density of the vacuum fluctuations S(ωa) as a function of L/λ.


  1. 1

    Dirac, P. A. M. The quantum theory of the emission and absorption of radiation. Proc. R. Soc. Lond. A 114, 243–265 (1927).

    ADS  Article  Google Scholar 

  2. 2

    Bethe, H. A. The electromagnetic shift of energy levels. Phys. Rev. 72, 339–341 (1947).

    ADS  Article  Google Scholar 

  3. 3

    Lamb, W. E. & Retherford, R. C. Fine structure of the hydrogen atom by a microwave method. Phys. Rev. 72, 241–243 (1947).

    ADS  Article  Google Scholar 

  4. 4

    Schwinger, J. On quantum-electrodynamics and the magnetic moment of the electron. Phys. Rev. 73, 416–417 (1948).

    ADS  Article  Google Scholar 

  5. 5

    Welton, T. Some observable effects of the quantum-mechanical fluctuation of the electromagnetic field. Phys. Rev. 74, 1157–1167 (1948).

    ADS  Article  Google Scholar 

  6. 6

    Lamoreaux, S. K. Casimir forces: Still surprising after 60 years. Phys. Today 60, 40–45 (February, 2007).

    Article  Google Scholar 

  7. 7

    Harris, D. Harnessing the quantum power of empty space. New Sci. 2852, 34–37 (2012).

    ADS  Article  Google Scholar 

  8. 8

    Hawking, S. W. Black hole explosions. Nature 248, 30–31 (1974).

    ADS  Article  Google Scholar 

  9. 9

    Unruh, W. G. Notes on black-hole evaporation. Phys. Rev. D 14, 870–892 (1976).

    ADS  Article  Google Scholar 

  10. 10

    Casimir, H. B. G. On the attraction between two perfectly conducting plates. Proc. K. Ned. Akad. Wet. B 51, 793–795 (1948).

    MATH  Google Scholar 

  11. 11

    Moore, G. T. Quantum theory of the electromagnetic field in a variable-length one-dimensional cavity. J. Math. Phys. 11, 2679–2691 (1970).

    ADS  Article  Google Scholar 

  12. 12

    Wilson, C. M. et al. Observation of the dynamical Casimir effect in a superconducting circuit. Nature 479, 376–379 (2011).

    ADS  Article  Google Scholar 

  13. 13

    Chan, H. B., Aksyuk, V. A., Kleiman, R. N., Bishop, D. J. & Capasso, F. Quantum mechanical actuation of microelectromechanical systems by the Casimir force. Science 291, 1941–1944 (2001).

    ADS  Article  Google Scholar 

  14. 14

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

    ADS  Article  Google Scholar 

  15. 15

    Astafiev, O., Pashkin, Yu. A., Nakamura, Y., Yamamoto, T. & Tsai, J. S. Quantum noise in the Josephson charge qubit. Phys. Rev. Lett. 93, 267007 (2004).

    ADS  Article  Google Scholar 

  16. 16

    Eschner, J., Raab, Ch., Schmidt-Kaler, F. & Blatt, R. Light interference from single atoms and their mirror images. Nature 413, 495–498 (2001).

    ADS  Article  Google Scholar 

  17. 17

    Dorner, U. & Zoller, P. Laser-driven atoms in half-cavities. Phys. Rev. A 66, 023816 (2002).

    ADS  Article  Google Scholar 

  18. 18

    Bushev, P. et al. Forces between a single atom and its distant mirror image. Phys. Rev. Lett. 92, 223602 (2004).

    ADS  Article  Google Scholar 

  19. 19

    Dubin, F. et al. Photon correlation versus interference of single-atom fluorescence in a half-cavity. Phys. Rev. Lett. 98, 183003 (2007).

    ADS  Article  Google Scholar 

  20. 20

    Glaetzle, A. W., Hammerer, K., Daley, A. J., Blatt, R. & Zoller, P. A single trapped atom in front of an oscillating mirror. Opt. Commun. 283, 758–765 (2010).

    ADS  Article  Google Scholar 

  21. 21

    Purcell, E. M. Spontaneous emission probabilities at radio frequencies. Phys. Rev. 69, 681 (1946).

    Article  Google Scholar 

  22. 22

    Kleppner, D. Inhibited spontaneous emission. Phys. Rev. Lett. 47, 233 (1981).

    ADS  Article  Google Scholar 

  23. 23

    DeMartini, F., Innocenti, G., Jacobovitz, G. R. & Mataloni, P. Anomalous spontaneous emission time in a microscopic optical cavity. Phys. Rev. Lett. 59, 2955–2958 (1987).

    ADS  Article  Google Scholar 

  24. 24

    Lee, M. Three-dimensional imaging of cavity vacuum with single atoms localized by a nanohole array. Nature Commun. 5, 3441 (2014).

    ADS  Article  Google Scholar 

  25. 25

    Reed, M.D. et al. Fast reset and surprising spontaneous emission of a superconducting qubit. Appl. Phys. Lett. 96, 203110 (2010).

    ADS  Article  Google Scholar 

  26. 26

    Kockum, A. F., Delsing, P. & Johansson, G. Designing frequency-dependent relaxation rates and Lamb shifts for a giant artificial atom. Phys. Rev. A 90, 013837 (2014).

    ADS  Article  Google Scholar 

  27. 27

    van Loo, A. F. et al. Photon-mediated interactions between distant artificial atoms. Science 342, 1494–1496 (2013).

    ADS  Article  Google Scholar 

  28. 28

    Astafiev, O. et al. Resonance fluorescence of a single artificial atom. Science 327, 840–843 (2010).

    ADS  Article  Google Scholar 

  29. 29

    Abdumalikov, A. A. et al. Electromagnetically induced transparency on a single artificial atom. Phys. Rev. Lett. 104, 193601 (2010).

    ADS  Article  Google Scholar 

  30. 30

    Hoi, I.-C. et al. Demonstration of a single-photon router in the microwave regime. Phys. Rev. Lett. 107, 073601 (2011).

    ADS  Article  Google Scholar 

  31. 31

    Hoi, I.-C. et al. Generation of nonclassical microwave states using an artificial atom in 1d open space. Phys. Rev. Lett. 108, 263601 (2012).

    ADS  Article  Google Scholar 

  32. 32

    Hoi, I.-C. et al. Giant cross–Kerr effect for propagating microwaves induced by an artificial atom. Phys. Rev. Lett. 111, 053601 (2013).

    ADS  Article  Google Scholar 

  33. 33

    Hoi, I.-C. et al. Microwave quantum optics with an artificial atom in one-dimensional open space. New J. Phys. 15, 025011 (2013).

    ADS  Article  Google Scholar 

  34. 34

    Zheng, H., Gauthier, D. J. & Baranger, H. U. Waveguide-QED-based photonic quantum computation. Phys. Rev. Lett. 111, 090502 (2013).

    ADS  Article  Google Scholar 

  35. 35

    Chang, D. E., Sorensen, A. S., Demler, E. A. & Lukin, M. D. A single-photon transistor using nanoscale surface plasmons. Nature Phys. 3, 807–812 (2007).

    ADS  Article  Google Scholar 

  36. 36

    Shen, J. T. & Fan, S. H. Coherent single photon transport in a one-dimensional waveguide coupled with superconducting quantum bits. Phys. Rev. Lett. 95, 213001 (2005).

    ADS  Article  Google Scholar 

  37. 37

    Lalumiere, K. et al. Input–output theory for waveguide QED with an ensemble of inhomogeneous atoms. Phys. Rev. A 88, 043806 (2013).

    ADS  Article  Google Scholar 

  38. 38

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

    ADS  Article  Google Scholar 

  39. 39

    Clerk, A. A., Devoret, M. H., Girvin, S. M., Marquardt, F. & Schoelkopf, R. J. Introduction to quantum noise, measurement and amplification. Rev. Mod. Phys. 82, 1155–1208 (2010).

    ADS  MathSciNet  Article  Google Scholar 

  40. 40

    Koshino, K. & Nakamura, Y. Control of the radiative level shift and linewidth of a superconducting artificial atom through a variable boundary condition. New J. Phys. 14, 043005 (2012).

    ADS  Article  Google Scholar 

  41. 41

    Wendin, G. & Shumeiko, V. S. Quantum bits with Josephson junctions. Low Temp. Phys. 33, 724–744 (2007).

    ADS  Article  Google Scholar 

  42. 42

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

    ADS  Article  Google Scholar 

  43. 43

    Peropadre, B. et al. Scattering of coherent states on a single artificial atom. New J. Phys. 15, 035009 (2013).

    ADS  Article  Google Scholar 

Download references


We acknowledge financial support from STINT, the Swedish Research Council, the European Union represented by the ERC and the EU project PROMISCE, NSERC of Canada, Industry Canada, and the Government of Ontario. We would also like to acknowledge J. Kimble, G. Milburn, T. Stace, J. M. Martinis, C. P. Sun and H. Dong for fruitful discussions.

Author information




I.-C.H., A.P., C.M.W. and P.D. designed and performed the experiment. A.F.K., L.T. and G.J. provided theoretical assistance. All authors contributed to the preparation of the manuscript.

Corresponding authors

Correspondence to P. Delsing or C. M. Wilson.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 644 kb)

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Hoi, IC., Kockum, A., Tornberg, L. et al. Probing the quantum vacuum with an artificial atom in front of a mirror. Nature Phys 11, 1045–1049 (2015).

Download citation

Further reading


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