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.

Laser cooling of optically trapped molecules


Ultracold molecules are ideal platforms for many important applications, ranging from quantum simulation1,2,3,4,5 and quantum information processing 6,7 to precision tests of fundamental physics2,8,9,10,11. Producing trapped, dense samples of ultracold molecules is a challenging task. One promising approach is direct laser cooling, which can be applied to several classes of molecules not easily assembled from ultracold atoms12,13. Here, we report the production of trapped samples of laser-cooled CaF molecules with densities of 8 × 107 cm−3 and at phase-space densities of 2 × 10−9, 35 times higher than for sub-Doppler-cooled samples in free space14. These advances are made possible by efficient laser cooling of optically trapped molecules to well below the Doppler limit, a key step towards many future applications. These range from ultracold chemistry to quantum simulation, where conservative trapping of cold and dense samples is desirable. In addition, the ability to cool optically trapped molecules opens up new paths towards quantum degeneracy.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Schematic of experimental apparatus and level diagram for sub-Doppler cooling of CaF.
Fig. 2: Loss rate of molecules trapped in the ODT.
Fig. 3: Dependence of sub-Doppler cooling and ODT loading on laser detuning.
Fig. 4: Loading of molecules into the ODT as a function of overlap time, τ, with the sub-Doppler light.
Fig. 5: Cooling of optically trapped molecules.


  1. 1.

    Micheli, A., Brennen, G. K. & Zoller, P. A toolbox for lattice-spin models with polar molecules. Nat. Phys. 2, 341–347 (2006).

    Article  Google Scholar 

  2. 2.

    Carr, L. D., DeMille, D., Krems, R. V. & Ye, J. Cold and ultracold molecules: science, technology and applications. New J. Phys. 11, 055049 (2009).

    ADS  Article  Google Scholar 

  3. 3.

    Pupillo, G. et al. Cold atoms and molecules in self-assembled dipolar lattices. Phys. Rev. Lett. 100, 050402 (2008).

    ADS  Article  Google Scholar 

  4. 4.

    Büchler, H. P. et al. Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential. Phys. Rev. Lett. 98, 060404 (2007).

    Article  Google Scholar 

  5. 5.

    Blackmore, J. A. et al. Ultracold molecules: a platform for quantum simulation. Preprint at (2018).

  6. 6.

    DeMille, D. Quantum computation with trapped polar molecules. Phys. Rev. Lett. 88, 067901 (2002).

    ADS  Article  Google Scholar 

  7. 7.

    Yelin, S. F., Kirby, K. & Côté, R. Schemes for robust quantum computation with polar molecules. Phys. Rev. A 74, 050301 (2006).

    ADS  Article  Google Scholar 

  8. 8.

    ACME Collaboration Order of magnitude smaller limit on the electric dipole moment of the electron. Science 343, 269–272 (2014).

    Article  Google Scholar 

  9. 9.

    Kara, D. M. et al. Measurement of the electrons electric dipole moment using YbF molecules: methods and data analysis. New J. Phys. 14, 103051 (2012).

    ADS  Article  Google Scholar 

  10. 10.

    Lim, J. et al. Laser cooled YbF molecules for measuring the electron’s electric dipole moment. Phys. Rev. Lett. 120, 123201 (2018).

    ADS  Article  Google Scholar 

  11. 11.

    Kozyryev, I. & Hutzler, N. R. Precision measurement of time-reversal symmetry violation with laser-cooled polyatomic molecules. Phys. Rev. Lett. 119, 133002 (2017).

    ADS  Article  Google Scholar 

  12. 12.

    Rosa, M. D. Laser-cooling molecules. Eur. Phys. J. D 31, 395–402 (2004).

    ADS  Article  Google Scholar 

  13. 13.

    Kozyryev, I., Baum, L., Matsuda, K. & Doyle, J. M. Proposal for laser cooling of complex polyatomic molecules. ChemPhysChem 17, 3641–3648 (2016).

    Article  Google Scholar 

  14. 14.

    Williams, H. J. et al. Magnetic trapping and coherent control of laser-cooled molecules. Phys. Rev. Lett. 120, 163201 (2018).

    ADS  Article  Google Scholar 

  15. 15.

    Yan, B. et al. Observation of dipolar spin-exchange interactions with lattice-confined polar molecules. Nature 501, 521–525 (2013).

    ADS  Article  Google Scholar 

  16. 16.

    Ospelkaus, S. et al. Quantum-state controlled chemical reactions of ultracold potassium-rubidium molecules. Science 327, 853–857 (2010).

    ADS  Article  Google Scholar 

  17. 17.

    Barry, J. F., McCarron, D. J., Norrgard, E. B., Steinecker, M. H. & DeMille, D. Magneto-optical trapping of a diatomic molecule. Nature 512, 286–289 (2014).

    ADS  Article  Google Scholar 

  18. 18.

    Norrgard, E., McCarron, D., Steinecker, M., Tarbutt, M. & DeMille, D. Sub-millikelvin dipolar molecules in a radio-frequency magneto-optical trap. Phys. Rev. Lett. 116, 063004 (2016).

    ADS  Article  Google Scholar 

  19. 19.

    Steinecker, M. H., McCarron, D. J., Zhu, Y. & DeMille, D. Improved radio-frequency magneto-optical trap of SrF molecules. ChemPhysChem 17, 3664–3669 (2016).

    Article  Google Scholar 

  20. 20.

    Truppe, S. et al. Molecules cooled below the Doppler limit. Nat. Phys. 13, 1173–1176 (2017).

    Article  Google Scholar 

  21. 21.

    Anderegg, L. et al. Radio frequency magneto-optical trapping of CaF with high density. Phys. Rev. Lett. 119, 103201 (2017).

    ADS  Article  Google Scholar 

  22. 22.

    McCarron, D. J., Steinecker, M. H., Zhu, Y. & DeMille, D. Magnetically-trapped molecules efficiently loaded from a molecular MOT. Preprint at (2017).

  23. 23.

    Stellmer, S., Pasquiou, B., Grimm, R. & Schreck, F. Laser cooling to quantum degeneracy. Phys. Rev. Lett. 110, 263003 (2013).

    ADS  Article  Google Scholar 

  24. 24.

    Hu, J. et al. Creation of a Bose-condensed gas of 87Rb by laser cooling. Science 358, 1078–1080 (2017).

    ADS  Article  Google Scholar 

  25. 25.

    Truppe, S. et al. An intense, cold, velocity-controlled molecular beam by frequency-chirped laser slowing. New J. Phys. 19, 022001 (2017).

    ADS  Article  Google Scholar 

  26. 26.

    Devlin, J. A. & Tarbutt, M. R. Three-dimensional doppler, polarization-gradient, and magneto-optical forces for atoms and molecules with dark states. New J. Phys. 18, 123017 (2016).

    ADS  Article  Google Scholar 

  27. 27.

    Grynberg, G. & Courtois, J.-Y. Proposal for a magneto-optical lattice for trapping atoms in nearly-dark states. Europhys. Lett. 27, 41–46 (1994).

    ADS  Article  Google Scholar 

  28. 28.

    Sievers, F. et al. Simultaneous sub-Doppler laser cooling of fermionic 6Li and 40K on the D 1 line: theory and experiment. Phys. Rev. A 91, 023426 (2015).

    ADS  Article  Google Scholar 

  29. 29.

    Burchianti, A. et al. Efficient all-optical production of large 6Li quantum gases using D 1 gray-molasses cooling. Phys. Rev. A 90, 043408 (2014).

    ADS  Article  Google Scholar 

  30. 30.

    Colzi, G. et al. Sub-Doppler cooling of sodium atoms in gray molasses. Phys. Rev. A 93, 023421 (2016).

    ADS  Article  Google Scholar 

  31. 31.

    Kozyryev, I. et al. Sisyphus laser cooling of a polyatomic molecule. Phys. Rev. Lett. 118, 173201 (2017).

    ADS  Article  Google Scholar 

  32. 32.

    Kosicki, M. B., Kedziera, D. & Zuchowski, P. S. Ab initio study of chemical reactions of cold SrF and CaF molecules with alkali-metal and alkaline-earth-metal atoms: the implications for sympathetic cooling. J. Phys. Chem. A 121, 4152–4159 (2017).

    Article  Google Scholar 

  33. 33.

    Lim, J., Frye, M. D., Hutson, J. M. & Tarbutt, M. R. Modeling sympathetic cooling of molecules by ultracold atoms. Phys. Rev. A 92, 053419 (2015).

    ADS  Article  Google Scholar 

  34. 34.

    Quéméner, G. & Bohn, J. L.. Shielding 2Σ ultracold dipolar molecular collisions with electric fields. Phys. Rev. A 93, 012704 (2016).

    ADS  Article  Google Scholar 

  35. 35.

    Schlosser, N., Reymond, G. & Grangier, P. Collisional blockade in microscopic optical dipole traps. Phys. Rev. Lett. 89, 023005 (2002).

    ADS  Article  Google Scholar 

  36. 36.

    Yavuz, D. D. et al. Fast ground state manipulation of neutral atoms in microscopic optical traps. Phys. Rev. Lett. 96, 063001 (2006).

    ADS  Article  Google Scholar 

  37. 37.

    Endres, M. et al. Atom-by-atom assembly of defect-free one-dimensional cold atom arrays. Science 354, 1024–1027 (2016).

    ADS  Article  Google Scholar 

  38. 38.

    Barredo, D., de Léséleuc, S., Lienhard, V., Lahaye, T. & Browaeys, A. An atom-by-atom assembler of defect-free arbitrary two-dimensional atomic arrays. Science 354, 1021–1023 (2016).

    ADS  Article  Google Scholar 

  39. 39.

    Vuletić, V., Chin, C., Kerman, A. J. & Chu, S. Degenerate Raman sideband cooling of trapped cesium atoms at very high atomic densities. Phys. Rev. Lett. 81, 5768–5771 (1998).

    ADS  Article  Google Scholar 

  40. 40.

    Roos, C. F. et al. Experimental demonstration of ground state laser cooling with electromagnetically induced transparency. Phys. Rev. Lett. 85, 5547–5550 (2000).

    ADS  Article  Google Scholar 

  41. 41.

    Kaufman, A. M., Lester, B. J. & Regal, C. A. Cooling a single atom in an optical tweezer to its quantum ground state. Phys. Rev. X 2, 041014 (2012).

    Google Scholar 

  42. 42.

    Thompson, J. D., Tiecke, T. G., Zibrov, A. S., Vuletić, V. & Lukin, M. D. Coherence and Raman sideband cooling of a single atom in an optical tweezer. Phys. Rev. Lett. 110, 133001 (2013).

    ADS  Article  Google Scholar 

Download references


This work was supported by the National Science Foundation (NSF) and Army Research Office (ARO). B.L.A. acknowledges support from NSF Graduate Research Fellowship Program. L.W.C. acknowledges support from Max Planck Harvard Research Center for Quantum Optics. We thank the Greiner group for lending us a 1,064-nm fibre amplifier.

Author information




All authors contributed to all aspects of this work.

Corresponding author

Correspondence to Loïc Anderegg.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

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

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Anderegg, L., Augenbraun, B.L., Bao, Y. et al. Laser cooling of optically trapped molecules. Nature Phys 14, 890–893 (2018).

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