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.

  • Letter
  • Published:

Entanglement-enhanced detection of single-photon scattering events



The ability to detect the interaction of light and matter at the single-particle level is becoming increasingly important for many areas of science and technology. The absorption or emission of a photon on a narrow transition of a trapped ion can be detected with near unit probability1,2, thereby enabling the realization of ultra-precise ion clocks3,4 and quantum information processing applications5. Extending this sensitivity to broad transitions is challenging due to the difficulty of detecting the rapid photon scattering events in this case. Here, we demonstrate a technique to detect the scattering of a single photon on a broad optical transition with high sensitivity. Our approach is to use an entangled state to amplify the tiny momentum kick an ion receives upon scattering a photon. The method should find applications in spectroscopy of atomic and molecular ions6,7,8,9 and quantum information processing.

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

Access options

Buy this article

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

Figure 1: Cat-state spectroscopy in phase space.
Figure 2: Experimental details.
Figure 3: Cat-state spectroscopy results.

Similar content being viewed by others


  1. Dehmelt, H. G. Mono-ion oscillator as potential ultimate laser frequency standard. IEEE Trans. Instrum. Meas. 31, 83–87 (1982).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  3. Rosenband, T. et al. Frequency ratio of Al+ and Hg+ single-ion optical clocks; metrology at the 17th decimal place. Science 319, 1808–1812 (2008).

    Article  ADS  Google Scholar 

  4. Chou, C., Hume, D., Koelemeij, J., Wineland, D. & Rosenband, T. Frequency comparison of two high-accuracy Al+ optical clocks. Phys. Rev. Lett. 104, 070802 (2010).

    Article  ADS  Google Scholar 

  5. Häffner, H., Roos, C. F. & Blatt, R. Quantum computing with trapped ions. Phys. Rep. 469, 155–203 (2008).

    Article  ADS  MathSciNet  Google Scholar 

  6. Nguyen, J. H. V. et al. Challenges of laser-cooling molecular ions. New J. Phys. 13, 063023 (2011).

    Article  ADS  Google Scholar 

  7. Mur-Petit, J. et al. Temperature-independent quantum logic for molecular spectroscopy. Phys. Rev. A 85, 022308 (2012).

    Article  ADS  Google Scholar 

  8. Leibfried, D. Quantum state preparation and control of single molecular ions. New J. Phys. 14, 023029 (2012).

    Article  ADS  Google Scholar 

  9. Ding, S. & Matsukevich, D. N. Quantum logic for the control and manipulation of molecular ions using a frequency comb. New J. Phys. 14, 023028 (2012).

    Article  ADS  Google Scholar 

  10. Wineland, D. J. & Itano, W. M. Laser cooling of atoms. Phys. Rev. A 20, 1521–1540 (1979).

    Article  ADS  Google Scholar 

  11. Larson, D. J., Bergquist, J. C., Bollinger, J. J., Itano, W. M. & Wineland, D. J. Sympathetic cooling of trapped ions: a laser-cooled two-species nonneutral ion plasma. Phys. Rev. Lett. 57, 70–73 (1986).

    Article  ADS  Google Scholar 

  12. Schmidt, P. O. et al. Spectroscopy using quantum logic. Science 309, 749–752 (2005).

    Article  ADS  Google Scholar 

  13. Hume, D. B. et al. Trapped-ion state detection through coherent motion. Phys. Rev. Lett. 107, 243902 (2011).

    Article  ADS  Google Scholar 

  14. Weiss, D. S., Young, B. C. & Chu, S. Precision measurement of the photon recoil of an atom using atomic interferometry. Phys. Rev. Lett. 70, 2706–2709 (1993).

    Article  ADS  Google Scholar 

  15. Clark, C. R., Goeders, J. E., Dodia, Y. K., Viteri, C. R. & Brown, K. R. Detection of single-ion spectra by Coulomb-crystal heating. Phys. Rev. A 81, 043428 (2010).

    Article  ADS  Google Scholar 

  16. Poyatos, J. F., Cirac, J. I., Blatt, R. & Zoller, P. Trapped ions in the strong-excitation regime: ion interferometry and nonclassical states. Phys. Rev. A 54, 1532–1540 (1996).

    Article  ADS  Google Scholar 

  17. Monroe, C. R., Meekhof, D. M., King, B. E. & Wineland, D. J. A ‘Schrodinger cat’ superposition state of an atom. Science 272, 1131–1136 (1996).

    Article  ADS  MathSciNet  Google Scholar 

  18. Chaturvedi, S., Sriram, M. S. & Srinivasan, V. Berry's phase for coherent states. J. Phys. A 20, L1071–L1075 (1987).

    Article  ADS  MathSciNet  Google Scholar 

  19. Turchette, Q. A. et al. Decoherence and decay of motional quantum states of a trapped atom coupled to engineered reservoirs. Phys. Rev. A 62, 053807 (2000).

    Article  ADS  Google Scholar 

  20. Munro, W. J., Nemoto, K., Milburn, G. J. & Braunstein, S. L. Weak-force detection with superposed coherent states. Phys. Rev. A 66, 023819 (2002).

    Article  ADS  Google Scholar 

  21. Jin, J. & Church, D. A. Precision lifetimes for the Ca+ 4p2P levels: experiment challenges theory at the 1% level. Phys. Rev. Lett. 70, 3213–3216 (1993).

    Article  ADS  Google Scholar 

  22. Ramm, M., Pruttivarasin, T., Kokish, M., Talukdar, I. & Häffner, H. Precision measurement method for branching fractions of excited P1/2 states applied to 40Ca+. Preprint at (2013).

  23. Haljan, P. C., Brickman, K-A., Deslauriers, L., Lee, P. J. & Monroe, C. Spin-dependent forces on trapped ions for phase-stable quantum gates and entangled states of spin and motion. Phys. Rev. Lett. 94, 153602 (2005).

    Article  ADS  Google Scholar 

  24. Itano, W. M. et al. Quantum projection noise: population fluctuations in two-level systems. Phys. Rev. A 47, 3554–3570 (1993).

    Article  ADS  Google Scholar 

  25. Kirchmair, G. et al. Deterministic entanglement of ions in thermal states of motion. New J. Phys. 11, 023002 (2009).

    Article  ADS  Google Scholar 

  26. Lucas, D. M. et al. Isotope-selective photoionization for calcium ion trapping. Phys. Rev. A 69, 012711 (2004).

    Article  ADS  Google Scholar 

Download references


This work was supported by the European Commission via the integrated project Atomic QUantum TEchnologies and a Marie Curie International Incoming Fellowship.

Author information

Authors and Affiliations



C.R. conceived and designed the experiments. C.H., B.L., P.J., R.G. and C.R. performed the experiments. C.H., B.L. and C.R. analysed the data. C.H., B.L., R.G., R.B. and C.R. contributed materials and analysis tools. C.H., B.L. and C.R. wrote the paper.

Corresponding author

Correspondence to C. F. Roos.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 521 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hempel, C., Lanyon, B., Jurcevic, P. et al. Entanglement-enhanced detection of single-photon scattering events. Nature Photon 7, 630–633 (2013).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


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