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  • Letter
  • Open Access

Efficient associative ionization of ultracold lithium and the long-lived Li2+

N. Joshi1,*,†, Vaibhav Mahendrakar1,*, M. Niranjan1,*, Raghuveer Singh Yadav1, E. Krishnakumar1, A. Pandey2, R. Vexiau2, O. Dulieu2, and S. A. Rangwala1,‡

  • *These authors contributed equally to this work.
  • †Contact author: njoshi@rri.res.in
  • ‡Contact author: sarangwala@rri.res.in
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Phys. Rev. Research 8, L032008 – Published 17 July, 2026

DOI: https://doi.org/10.1103/z7xy-hmlb

Abstract

We report on the efficient production of Li2+ ions in a magneto-optical trap (MOT) of Li atoms prepared in an ensemble of 2S, 2P, and 3S states. A linear Paul trap surrounding the MOT is used to trap and investigate the time evolution of the ion populations. Associative ionization of Li(2P3/2) and Li(3S1/2) atoms, with a giant cross section of ∼2.2×106a02, is the dominant Li2+ production channel. Li2+ decays to Li+ via photodissociation and also in the absence of light, which are investigated experimentally and theoretically. A fraction of the Li2+ ions are long-lived in the presence of the MOT light, implying that they are deeply bound and hence immune to dissociation, which opens up the possibility for studying Li2+ molecular ion interactions with alkali atoms.

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References (62)

  1. W. W. Smith, O. P. Makarov, and J. Lin, Cold ion–neutral collisions in a hybrid trap, J. Mod. Opt. 52, 2253 (2005).
  2. A. T. Grier, M. Cetina, F. Oručević, and V. Vuletić, Observation of cold collisions between trapped ions and trapped atoms, Phys. Rev. Lett. 102, 223201 (2009).
  3. C. Zipkes, S. Palzer, C. Sias, and M. Köhl, A trapped single ion inside a Bose–Einstein condensate, Nature (London) 464, 388 (2010).
  4. F. H. J. Hall, M. Aymar, N. Bouloufa-Maafa, O. Dulieu, and S. Willitsch, Light-assisted ion-neutral reactive processes in the cold regime: Radiative molecule formation versus charge exchange, Phys. Rev. Lett. 107, 243202 (2011).
  5. S. Schmid, A. Härter, A. Frisch, S. Hoinka, and J. H. Denschlag, An apparatus for immersing trapped ions into an ultracold gas of neutral atoms, Rev. Sci. Instrum. 83, 053108 (2012).
  6. K. Ravi, S. Lee, A. Sharma, G. Werth, and S. A. Rangwala, Combined ion and atom trap for low-temperature ion–atom physics, Appl. Phys. B 107, 971 (2012).
  7. S. Haze, S. Hata, M. Fujinaga, and T. Mukaiyama, Observation of elastic collisions between lithium atoms and calcium ions, Phys. Rev. A 87, 052715 (2013).
  8. H. López, B. Höltkemeier, J. Glässel, P. Weckesser, M. Weidemüller, T. Best, E. Endres, and R. Wester, Sympathetic cooling of OH− ions using ultracold Rb atoms in a dark SPOT, in Ion Traps for Tomorrow's Applications, edited by M. Knoop, I. Marzoli, and G. Morigi (IOS Press, Amsterdam / Oxford, 2015), pp. 279–287.
  9. E. R. Hudson, Sympathetic cooling of molecular ions with ultracold atoms, EPJ Tech. Instrum. 3, 8 (2016).
  10. Z. Meir, T. Sikorsky, R. Ben-shlomi, N. Akerman, M. Pinkas, Y. Dallal, and R. Ozeri, Experimental apparatus for overlapping a ground-state cooled ion with ultracold atoms, J. Mod. Opt. 65, 501 (2018).
  11. S. Jyothi, K. N. Egodapitiya, B. Bondurant, Z. Jia, E. Pretzsch, P. Chiappina, G. Shu, and K. R. Brown, A hybrid ion-atom trap with integrated high resolution mass spectrometer, Rev. Sci. Instrum. 90, 103201 (2019).
  12. H. Hirzler, T. Feldker, H. Fürst, N. V. Ewald, E. Trimby, R. S. Lous, J. D. A. Espinoza, M. Mazzanti, J. Joger, and R. Gerritsma, Experimental setup for studying an ultracold mixture of trapped Yb+–6Li, Phys. Rev. A 102, 033109 (2020).
  13. J. Schmidt, P. Weckesser, F. Thielemann, T. Schaetz, and L. Karpa, Optical traps for sympathetic cooling of ions with ultracold neutral atoms, Phys. Rev. Lett. 124, 053402 (2020).
  14. C. Veit, N. Zuber, O. A. Herrera-Sancho, V. S. V. Anasuri, T. Schmid, F. Meinert, R. Löw, and T. Pfau, Pulsed ion microscope to probe quantum gases, Phys. Rev. X 11, 011036 (2021).
  15. M. Tomza, K. Jachymski, R. Gerritsma, A. Negretti, T. Calarco, Z. Idziaszek, and P. S. Julienne, Cold hybrid ion-atom systems, Rev. Mod. Phys. 91, 035001 (2019).
  16. S. Schiller, Precision spectroscopy of molecular hydrogen ions: An introduction, Contemp. Phys. 63, 247 (2022).
  17. A. Pandey, M. Niranjan, N. Joshi, S. A. Rangwala, R. Vexiau, and O. Dulieu, Interaction potentials and ultracold scattering cross sections for the Li+7−Li7 ion-atom system, Phys. Rev. A 101, 052702 (2020).
  18. S. Jyothi, T. Ray, S. Dutta, A. R. Allouche, R. Vexiau, O. Dulieu, and S. A. Rangwala, Photodissociation of trapped Rb2+: Implications for simultaneous trapping of atoms and molecular ions, Phys. Rev. Lett. 117, 213002 (2016).
  19. A. Mohammadi, A. Krükow, A. Mahdian, M. Deiß, J. Pérez-Ríos, H. da Silva, M. Raoult, O. Dulieu, and J. H. Denschlag, Life and death of a cold BaRb+ molecule inside an ultracold cloud of Rb atoms, Phys. Rev. Res. 3, 013196 (2021).
  20. N. Bjerre and S. R. Keiding, Long-range ion-atom interactions studied by field-dissociation spectroscopy of molecular ions, Phys. Rev. Lett. 56, 1459 (1986).
  21. T. Niederprüm, O. Thomas, T. Manthey, T. M. Weber, and H. Ott, Giant cross section for molecular ion formation in ultracold Rydberg gases, Phys. Rev. Lett. 115, 013003 (2015).
  22. Details about the instrument will be reported in a separate publication.
  23. P. Polak-Dingels, J. Keller, J. Weiner, J.-C. Gauthier, and N. Bras, Observation of laser-induced associative ionization in crossed-beam Na + Li collisions, Phys. Rev. A 24, 1107 (1981).
  24. P. Polak-Dingels, J. F. Delpech, and J. Weiner, Observation of structure in laser-induced Penning and associative ionization in crossed-beam Na + Na collisions, Phys. Rev. Lett. 44, 1663 (1980).
  25. X. Urbain, A. Cornet, F. Brouillard, and A. Giusti-Suzor, Dynamics of an elementary bond-forming process: Associative ionization in H(1s) + H(2s) collisions, Phys. Rev. Lett. 66, 1685 (1991).
  26. A. V. Hellfeld, J. Caddick, and J. Weiner, Observation of laser-induced Penning and associative ionization in Li-Li collisions, Phys. Rev. Lett. 40, 1369 (1978).
  27. E. Babenko, C. Tapalian, and W. W. Smith, Associative ionization in laser-excited sodium 3p + 3d collisions, Chem. Phys. Lett. 244, 121 (1995).
  28. C. Gabbanini, M. Biagini, S. Gozzini, A. Lucchesini, and L. Moi, Associative ionization in collisions between Na(3P3/2) and Cs(6P3/2), Phys. Rev. A 43, 2311 (1991).
  29. M. W. McGeoch, R. E. Schlier, and G. K. Chawla, Associative ionization with cold Rydberg lithium atoms, Phys. Rev. Lett. 61, 2088 (1988).
  30. Y. Ono, I. Koyano, and I. Tanaka, Mass spectrometric detection of Cs2+ produced by associative ionization, J. Chem. Phys. 52, 5969 (1970).
  31. P. L. Gould, P. D. Lett, P. S. Julienne, W. D. Phillips, H. R. Thorsheim, and J. Weiner, Observation of associative ionization of ultracold laser-trapped sodium atoms, Phys. Rev. Lett. 60, 788 (1988).
  32. J. J. Blangé, J. M. Zijlstra, A. Amelink, X. Urbain, H. Rudolph, P. van der Straten, H. C. W. Beijerinck, and H. G. M. Heideman, Vibrational state distribution of Na2+ ions created in ultracold collisions, Phys. Rev. Lett. 78, 3089 (1997).
  33. J. Weiner, Cold and Ultracold Collisions in Quantum Microscopic and Mesoscopic Systems (Cambridge University Press, Cambridge, England, 2003).
  34. M. Schlagmüller, T. C. Liebisch, F. Engel, K. S. Kleinbach, F. Böttcher, U. Hermann, K. M. Westphal, A. Gaj, R. Löw, S. Hofferberth, T. Pfau, J. Pérez-Ríos, and C. H. Greene, Ultracold chemical reactions of a single Rydberg atom in a dense gas, Phys. Rev. X 6, 031020 (2016).
  35. S. K. Kanungo, J. D. Whalen, Y. Lu, T. C. Killian, F. B. Dunning, S. Yoshida, and J. Burgdörfer, Loss rates for high-n,49≲n≲150,5sns(3s1) Rydberg atoms excited in an Sr84 Bose-Einstein condensate, Phys. Rev. A 102, 063317 (2020).
  36. A. Pandey, R. Vexiau, L. G. Marcassa, O. Dulieu, and N. Bouloufa-Maafa, Ultracold charged atom-dimer collisions: State-selective charge exchange and three-body recombination, Phys. Rev. Res. 6, 043010 (2024).
  37. J. Pérez-Ríos, Electric-field dissociation of weakly bound molecular ions, Phys. Rev. A 104, L031302 (2021).
  38. T. Dieterle, M. Berngruber, C. Hölzl, R. Löw, K. Jachymski, T. Pfau, and F. Meinert, Inelastic collision dynamics of a single cold ion immersed in a Bose-Einstein condensate, Phys. Rev. A 102, 041301 (2020).
  39. See Supplemental Material at http://link.aps.org/supplemental/10.1103/z7xy-hmlb for description related to fluorescence detection of atoms in 2P and 3S atomic states, a description for the methodologies for the detection of trapped Li+ and Li2+ ions, variation of the associative ionization rate with atomic density and 813 nm laser intensity.
  40. P. Kumar and V. Natarajan, Precise measurement of hyperfine structure in the 3S1/2 state of Li7, Sci. Rep. 7, 13204 (2017).
  41. A. Drakoudis, M. Söllner, and G. Werth, Instabilities of ion motion in a linear Paul trap, Int. J. Mass Spectrom. 252, 61 (2006).
  42. M. Sinhal and S. Willitsch, Molecular-ion quantum technologies, in Photonic Quantum Technologies: Science and Applications, edited by M. Benyoucef (Wiley-VCH, Weinheim, Germany, 2023), Vol. 1, p. 305.
  43. F. G. Major, V. N. Gheorghe, and G. Werth, Charged Particle Traps: Physics and Techniques of Charged Particle Field Confinement (Springer Science & Business Media, Berlin, Heidelberg, 2005), Vol. 37.
  44. X. Zhao, V. L. Ryjkov, and H. A. Schuessler, Parametric excitations of trapped ions in a linear RF ion trap, Phys. Rev. A 66, 063414 (2002).
  45. B. A. Collings, W. R. Stott, and F. A. Londry, Resonant excitation in a low-pressure linear ion trap, J. Am. Soc. Mass Spectrom. 14, 622 (2003).
  46. N. Šibalić, J. D. Pritchard, C. S. Adams, and K. J. Weatherill, Arc: An open-source library for calculating properties of alkali Rydberg atoms, Comput. Phys. Commun. 220, 319 (2017).
  47. P. Oxley and P. Collins, Frequency stabilization of multiple lasers and Rydberg atom spectroscopy, Appl. Phys. B 101, 23 (2010).
  48. M. Aymar and O. Dulieu, Calculation of accurate permanent dipole moments of the lowest 1,3Σ+ states of heteronuclear alkali dimers using extended basis sets, J. Chem. Phys. 122, 204302 (2005).
  49. R. Vexiau, D. Borsalino, M. Lepers, A. Orbán, M. Aymar, O. Dulieu, and N. Bouloufa-Maafa, Dynamic dipole polarizabilities of heteronuclear alkali dimers: Optical response, trapping and control of ultracold molecules, Int. Rev. Phys. Chem. 36, 709 (2017).
  50. O. Dulieu, A. Giusti-Suzor, and F. Masnou-Seeuws, Theoretical treatment of the associative ionization reaction between two laser-excited sodium atoms. Direct and indirect processes, J. Phys. B: At. Mol. Opt. Phys. 24, 4391 (1991).
  51. O. Dulieu, S. Magnier, and F. Masnou-Seeuws, Doubly-excited states for the Na2 molecule: Application to the dynamics of the associative ionization reaction, Z. Phys. D:At. Mol. Clusters 32, 229 (1994).
  52. O. Dulieu, Application of quantum defect theory to the associative ionisation reaction between two laser-excited sodium atoms, in Topics in Atomic and Nuclear Collisions, edited by B. Remaud, A. Calboreanu, and V. Zoran (Springer, New York, 1994), pp. 291–301.
  53. M. L. Trachy, G. Veshapidze, M. H. Shah, H. U. Jang, and B. D. DePaola, Photoassociation in cold atoms via ladder excitation, Phys. Rev. Lett. 99, 043003 (2007).
  54. C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour, Creation of polar and nonpolar ultra-long-range Rydberg molecules, Phys. Rev. Lett. 85, 2458 (2000).
  55. M. A. Bellos, R. Carollo, J. Banerjee, E. E. Eyler, P. L. Gould, and W. C. Stwalley, Excitation of weakly bound molecules to trilobitelike Rydberg states, Phys. Rev. Lett. 111, 053001 (2013).
  56. H. Hirzler, R. S. Lous, E. Trimby, J. Pérez-Ríos, A. Safavi-Naini, and R. Gerritsma, Observation of chemical reactions between a trapped ion and ultracold Feshbach dimers, Phys. Rev. Lett. 128, 103401 (2022).
  57. M. Deiß, S. Willitsch, and J. H. Denschlag, Cold trapped molecular ions and hybrid platforms for ions and neutral particles, Nat. Phys. 20, 713 (2024).
  58. S. Miyake, C. D. Gay, and P. C. Stancil, Rovibrationally resolved photodissociation of HeH+, Astrophys. J. 735, 21 (2011).
  59. S. Chu, L. Hollberg, J. E. Bjorkholm, A. Cable, and A. Ashkin, Three-dimensional viscous confinement and cooling of atoms by resonance radiation pressure, Phys. Rev. Lett. 55, 48 (1985).
  60. N. Kurz, Kinematically complete multiphoton ionization studies on optically trapped Li6 and 6Li2 created by single-color photoassociation, Ph.D. thesis, Ruprecht-Karls-Universität Heidelberg, 2021.
  61. N. Joshi, M. Niranjan, A. Pandey, O. Dulieu, R. Côté, and S. A. Rangwala, Homonuclear ion-atom collisions: Application to Li+−Li, Phys. Rev. A 105, 063311 (2022).
  62. S. Ghosh, T. Sahoo, M. Baer, and S. Adhikari, Charge transfer processes for H + H2+ reaction employing coupled 3D wavepacket approach on beyond Born–Oppenheimer based ab initio constructed diabatic potential energy surfaces, J. Phys. Chem. A 125, 731 (2021).

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Phys. Rev. Research 8, L032008– Published 17 July, 2026
  • Received 28 August 2024
  • Revised 25 February 2026
  • Accepted 10 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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