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.

Quantum logic detection of collisions between single atom–ion pairs


Studies of interactions between a single pair of atoms in a quantum state are a corner-stone of quantum chemistry, yet the number of demonstrated techniques that enable the observation and control of the outcome of a single collision is still small. Here we demonstrate a technique to study interactions between an ultracold neutral atom and a cold ion using quantum logic. We measure the inelastic release of hyperfine energy in a collision between an ultracold rubidium atom and isotopes of singly ionized strontium that we do not have experimental control over. We detect the collision outcome and measure the inelastic rate of the chemistry ion by reading the motional state of a logic ion qubit in a single shot. Our work extends the toolbox for studying elastic, inelastic and reactive chemical processes with existing experimental tools, especially for atomic and molecular ions for which direct laser cooling and state detection are unavailable.

Your institute does not have access to this article

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Logic detection of exothermic processes.
Fig. 2: Experimental set-up.
Fig. 3: Logic detection of hyperfine-changing collisions.

Data availability

Source data are provided with this paper. Other data that support the findings of this study are available from the corresponding author on reasonable request.


  1. Szabo, A. & Ostlund, N. Modern Quantum Chemistry (Dover, 1996).

    Google Scholar 

  2. Friesner, R. A. Ab initio quantum chemistry: methodology and applications. Proc. Natl Acad. Sci. USA 102, 6648–6653 (2005).

    ADS  MATH  Article  Google Scholar 

  3. Abrams, D. S. & Lloyd, S. Quantum algorithm providing exponential speed increase for finding eigenvalues and eigenvectors. Phys. Rev. Lett. 83, 5162 (1999).

    ADS  Article  Google Scholar 

  4. Chin, C., Grimm, R., Julienne, P. S. & Tiesinga, E. Feshbach resonances in ultracold gases. Rev. Mod. Phys. 82, 1225 (2010).

    ADS  Article  Google Scholar 

  5. Paliwal, P. et al. Determining the nature of quantum resonances by probing elastic and reactive scattering in cold collisions. Nat. Chem. 13, 94–98 (2021).

    Article  Google Scholar 

  6. Tomza, M. et al. Cold hybrid ion-atom systems. Rev. Mod. Phys. 91, 035001 (2019).

    ADS  MathSciNet  Article  Google Scholar 

  7. Meir, Z. et al. Experimental apparatus for overlapping a ground-state cooled ion with ultracold atoms. J. Mod. Opt. 65, 501–519 (2018).

    ADS  MathSciNet  Article  Google Scholar 

  8. Sikorsky, T., Meir, Z., Ben-shlomi, R., Akerman, N. & Ozeri, R. Spin-controlled atom-ion chemistry. Nat. Commun. 9, 920 (2018).

    ADS  Article  Google Scholar 

  9. Sikorsky, T. et al. Phase locking between different partial waves in atom-ion spin-exchange collisions. Phys. Rev. Lett. 121, 173402 (2018).

    ADS  Article  Google Scholar 

  10. Major, F. G. & Dehmelt, H. G. Exchange-collision technique for the rf spectroscopy of stored ions. Phys. Rev. 170, 91 (1968).

    ADS  Article  Google Scholar 

  11. Feldker, T. et al. Buffer gas cooling of a trapped ion to the quantum regime. Nat. Phys. 16, 413–416 (2020).

    Article  Google Scholar 

  12. Tscherbul, T. V., Brumer, P. & Buchachenko, A. A. Spin-orbit interactions and quantum spin dynamics in cold ion-atom collisions. Phys. Rev. Lett. 117, 143201 (2016).

    ADS  Article  Google Scholar 

  13. Ratschbacher, L., Zipkes, C., Sias, C. & Köhl, M. Controlling chemical reactions of a single particle. Nat. Phys. 8, 649–652 (2012).

    Article  Google Scholar 

  14. Rellergert, W. G. et al. Measurement of a large chemical reaction rate between ultracold closed-shell 40Ca atoms and open-shell 174Yb+ ions held in a hybrid atom-ion trap. Phys. Rev. Lett. 107, 243201 (2011).

    ADS  Article  Google Scholar 

  15. Ravi, K., Lee, S., Sharma, A., Werth, G. & Rangwala, S. A. Cooling and stabilization by collisions in a mixed ion-atom system. Nat. Commun. 3, 1126 (2012).

    ADS  Article  Google Scholar 

  16. Li, H. et al. Photon-mediated charge-exchange reactions between 39K atoms and 40Ca+ ions in a hybrid trap. Phys. Chem. Chem. Phys. 22, 10870–10881 (2020).

    ADS  Article  Google Scholar 

  17. Mahdian, A., Krükow, A. & Denschlag, J. H. Direct observation of swap cooling in atom-ion collisions. N. J. Phys. 23, 065008 (2021).

    Article  Google Scholar 

  18. Ben-shlomi, R. et al. High-energy-resolution measurements of an ultracold-atom-ion collisional cross section. Phys. Rev. A 103, 032805 (2021).

    ADS  Article  Google Scholar 

  19. Hall, F. H. J., Aymar, M., Bouloufa-Maafa, N., Dulieu, O. & Willitsch, S. Light-assisted ion-neutral reactive processes in the cold regime: radiative molecule formation versus charge exchange. Phys. Rev. Lett. 107, 243202 (2011).

    ADS  Article  Google Scholar 

  20. Mohammadi, A. et al. Life and death of a cold BaRb+ molecule inside an ultracold cloud of Rb atoms. Phys. Rev. Res. 3, 013196 (2021).

    Article  Google Scholar 

  21. Haze, S., Sasakawa, M., Saito, R., Nakai, R. & Mukaiyama, T. Cooling dynamics of a single trapped ion via elastic collisions with small-mass atoms. Phys. Rev. Lett. 120, 043401 (2018).

    ADS  Article  Google Scholar 

  22. Zipkes, C., Palzer, S., Ratschbacher, L., Sias, C. & Köhl, M. Cold heteronuclear ‘atom-ion collisions’. Phys. Rev. Lett. 105, 133201 (2010).

    ADS  Article  Google Scholar 

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

    ADS  Article  Google Scholar 

  24. Wolf, F. et al. Non-destructive state detection for quantum logic spectroscopy of molecular ions. Nature 530, 457–460 (2016).

    ADS  Article  Google Scholar 

  25. Sinhal, M., Meir, Z., Najafian, K., Hegi, G. & Willitsch, S. Quantum-nondemolition state detection and spectroscopy of single trapped molecules. Science 367, 1213–1218 (2020).

    ADS  Article  Google Scholar 

  26. Lin, Y., Leibrandt, D. R., Leibfried, D. & Chou, C. Quantum entanglement between an atom and a molecule. Nature 581, 273–277 (2020).

    ADS  Article  Google Scholar 

  27. Chou, C. W. et al. Frequency-comb spectroscopy on pure quantum states of a single molecular ion. Science 367, 1458–1461 (2020).

    ADS  Article  Google Scholar 

  28. Brewer, S. M. et al. 27Al+ quantum-logic clock with a systematic uncertainty below 10−18. Phys. Rev. Lett. 123, 033201 (2019).

    ADS  Article  Google Scholar 

  29. Gebert, F. et al. Precision isotope shift measurements in calcium ions using quantum logic detection schemes. Phys. Rev. Lett. 115, 053003 (2015).

    ADS  Article  Google Scholar 

  30. Kienzler, D. et al. Quantum logic spectroscopy with ions in thermal motion. Phys. Rev. X 10, 021012 (2020).

    Google Scholar 

  31. Micke, P. et al. Coherent laser spectroscopy of highly charged ions using quantum logic. Nature 578, 60–65 (2020).

    ADS  Article  Google Scholar 

  32. Wan, Y. et al. Precision spectroscopy by photon-recoil signal amplification. Nat. Commun. 5, 3096 (2014).

    ADS  Article  Google Scholar 

  33. Gebert, F. et al. Precision isotope shift measurements in calcium ions using quantum logic detection schemes. Phys. Rev. Lett. 115, 053003 (2015).

    ADS  Article  Google Scholar 

  34. Hall, F. H. J. & Willitsch, S. Millikelvin reactive collisions between sympathetically cooled molecular ions and laser-cooled atoms in an ion-atom hybrid trap. Phys. Rev. Lett. 109, 233202 (2012).

    ADS  Article  Google Scholar 

  35. Najafian, K., Meir, Z., Sinhal, M. & Willitsch, S. Identification of molecular quantum states using phase-sensitive forces. Nat. Commun. 11, 4470 (2020).

    ADS  Article  Google Scholar 

  36. Meir, Z., Hegi, G., Najafian, K., Sinhala, M. & Willitsch, S. State-selective coherent motional excitation as a new approach for the manipulation, spectroscopy and state-to-state chemistry of single molecular ions. Faraday Discuss. 217, 561–583 (2019).

    ADS  Article  Google Scholar 

  37. Tomza, M. & Lisaj, M. Interactions and charge-transfer dynamics of an Al+ ion immersed in ultracold Rb and Sr atoms. Phys. Rev. A 101, 012705 (2020).

    ADS  Article  Google Scholar 

  38. Cetina, M., Grier, A. T. & Vuletić, V. Micromotion-induced limit to atom-ion sympathetic cooling in Paul traps. Phys. Rev. Lett. 109, 253201 (2012).

    ADS  Article  Google Scholar 

  39. Côté, R. Ultracold hybrid atom-ion systems. Adv. Atom. Molec. Opt. Phys. 65, 67–126 (2016).

  40. Wesenberg, J. H. et al. Fluorescence during Doppler cooling of a single trapped atom. Phys. Rev. A 76, 053416 (2007).

    ADS  Article  Google Scholar 

  41. Drewsen, M., Mortensen, A., Martinussen, R., Staanum, P. & Sørensen, J. L. Nondestructive identification of cold and extremely localized single molecular ions. Phys. Rev. Lett. 93, 243201 (2004).

    ADS  Article  Google Scholar 

  42. Pinkas, M. et al. Effect of ion-trap parameters on energy distributions of ultra-cold atom-ion mixtures. N. J. Phys. 22, 013047 (2020).

    Article  Google Scholar 

  43. Côté, R. & Simbotin, I. Signature of the s -wave regime high above ultralow temperatures. Phys. Rev. Lett. 121, 173401 (2018).

    ADS  Article  Google Scholar 

  44. Tomza, M., Koch, C. P. & Moszynski, R. Cold interactions between an Yb+ ion and a Li atom: prospects for sympathetic cooling, radiative association, and Feshbach resonances. Phys. Rev. A 91, 042706 (2015).

    ADS  Article  Google Scholar 

  45. Weckesser, P. et al. Observation of Feshbach resonances between a single ion and ultracold atoms. Preprint at (2021).

  46. Bermudez, A., Schindler, P., Monz, T., Blatt, R. & Müller, M. Micromotion-enabled improvement of quantum logic gates with trapped ions. N. J. Phys. 19, 113038 (2017).

    Article  Google Scholar 

  47. Zipkes, C., Ratschbacher, L., Sias, C. & Köhl, M. Kinetics of a single trapped ion in an ultracold buffer gas. N. J. Phys. 13, 053020 (2011).

    Article  Google Scholar 

  48. Berkeland, D. J., Miller, J. D., Bergquist, J. C., Itano, W. M. & Wineland, D. J. Minimization of ion micromotion in a Paul trap. J. Appl. Phys. 83, 5025 (1998).

    ADS  Article  Google Scholar 

  49. Wübbena, J. B., Amairi, S., Mandel, O. & Schmidt, P. O. Sympathetic cooling of mixed-species two-ion crystals for precision spectroscopy. Phys. Rev. A 85, 043412 (2012).

    ADS  Article  Google Scholar 

Download references


We thank Z. Meir for useful comments on the manuscript. This work was supported by the Israeli Science Foundation, the Israeli Ministry of Science, Technology and Space and the Minerva Stiftung.

Author information

Authors and Affiliations



O.K., M.P., N.A. and R.O. contributed to the experimental design, construction, discussions and wrote the manuscript. O.K. collected the data and analysed the results. O.K. claims responsibility for all figures.

Corresponding author

Correspondence to Or Katz.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Physics thanks the anonymous reviewers for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Detection efficiency of electron shelving technique and its extension to additional configurations.

(a) The probability P(1) to measure the ion in the S, electronic ground-state, (bright) after a single shelving π-pulse of duration Tπ, following a single exothermic process releasing a total energy ΔE. For energetic processes (ΔEη2ω1z) and low beam power (ωz1Tπ 1) the detection of hot events approaches unity. Variation of the pulse duration Tπ implies simultaneous change of the Rabi frequency and pulse duration. (b) Detection efficiency of two pulses of electron shelving in the low beam power limit with the experimental parameters. A tilted beam (red) features sharper detection curve with respect to a beam co-linear with the trap axis (blue, denoted as the ‘base configuration’ in this analysis) that is sensitive to motion only along that axis. Black arrow marks the energy of hyperfine-changing collision studied in the experimental realization. (c)-(e) Extensions of the base configuration. (c) Variation of the the axial trap frequency enables detection of exothermic processes releasing energy below kB × (1 mK) at standard trap frequencies. (d) Configurations with unbalanced masses change the detection probability for exothermic process via scaling of the parameters ξz1, ξz2 [c.f. Eq. (5)-(6))]. Top: variation of the atom to chemistry-ion mass ratio for a fixed \({m}_{{{{\rm{i}}}}}^{L}={m}_{{{{\rm{i}}}}}^{c}\). Bottom: variation of the chemistry-ion to logic-ion mass ratio for a fixed \({m}_{{{{\rm{i}}}}}^{L}\) and \({m}_{{{{\rm{a}}}}}={m}_{{{{\rm{i}}}}}^{L}\). (e). Detection of elastic and endothermic collisional processes. An atom with kinetic energy Ea and moving perpendicular to the beam direction can scatter and generate motion of the crystal along the axis detected by the shelving beam (light-blue curve) in the base configuration. An endothermic process which converts a kinetic energy ΔE into internal one can be detected efficiently by varying the kinetic energy of the atom near Ea = 2ΔE (brown curve). Data in (a)-(e) is calculated numerically.

Source data

Supplementary information

Supplementary Information

Supplementary Notes 1 and 2 and Fig. 1.

Source data

Source Data Fig. 2

Data for Fig. 2d.

Source Data Fig. 3

Data for Fig. 3.

Source Data Extended Data Fig. 1

Data for Extended Data Fig. 1.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Katz, O., Pinkas, M., Akerman, N. et al. Quantum logic detection of collisions between single atom–ion pairs. Nat. Phys. 18, 533–537 (2022).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

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