Skip to main content

Thank you for visiting nature.com. 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.

Dipolar evaporation of reactive molecules to below the Fermi temperature

Abstract

The control of molecules is key to the investigation of quantum phases, in which rich degrees of freedom can be used to encode information and strong interactions can be precisely tuned1. Inelastic losses in molecular collisions2,3,4,5, however, have greatly hampered the engineering of low-entropy molecular systems6. So far, the only quantum degenerate gas of molecules has been created via association of two highly degenerate atomic gases7,8. Here we use an external electric field along with optical lattice confinement to create a two-dimensional Fermi gas of spin-polarized potassium–rubidium (KRb) polar molecules, in which elastic, tunable dipolar interactions dominate over all inelastic processes. Direct thermalization among the molecules in the trap leads to efficient dipolar evaporative cooling, yielding a rapid increase in phase-space density. At the onset of quantum degeneracy, we observe the effects of Fermi statistics on the thermodynamics of the molecular gas. These results demonstrate a general strategy for achieving quantum degeneracy in dipolar molecular gases in which strong, long-range and anisotropic dipolar interactions can drive the emergence of exotic many-body phases, such as interlayer pairing and p-wave superfluidity.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Experimental setup.
Fig. 2: Long-lived polar molecules in 2D.
Fig. 3: Tuning strong dipolar elastic interactions in a 2D molecular gas.
Fig. 4: Evaporative cooling to the quantum degenerate regime.

Data availability

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

References

  1. 1.

    Bohn, J. L., Rey, A. M. & Ye, J. Cold molecules: progress in quantum engineering of chemistry and quantum matter. Science 357, 1002–1010 (2017).

    ADS  MathSciNet  CAS  PubMed  MATH  Google Scholar 

  2. 2.

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

    ADS  CAS  PubMed  Google Scholar 

  3. 3.

    Ni, K.-K. et al. Dipolar collisions of polar molecules in the quantum regime. Nature 464, 1324–1328 (2010).

    ADS  CAS  PubMed  Google Scholar 

  4. 4.

    Guo, M. et al. Dipolar collisions of ultracold ground-state bosonic molecules. Phys. Rev. X 8, 041044 (2018).

    CAS  Google Scholar 

  5. 5.

    Gregory, P. D. et al. Sticky collisions of ultracold RbCs molecules. Nat. Commun. 10, 3104 (2019).

    ADS  PubMed  PubMed Central  Google Scholar 

  6. 6.

    Moses, S. A. et al. Creation of a low-entropy quantum gas of polar molecules in an optical lattice. Science 350, 659–662 (2015).

    ADS  CAS  PubMed  Google Scholar 

  7. 7.

    De Marco, L. et al. A degenerate Fermi gas of polar molecules. Science 363, 853–856 (2019).

    ADS  PubMed  Google Scholar 

  8. 8.

    Tobias, W. G. et al. Thermalization and sub-Poissonian density fluctuations in a degenerate molecular Fermi gas. Phys. Rev. Lett. 124, 033401 (2020).

    ADS  CAS  PubMed  Google Scholar 

  9. 9.

    André, A. et al. A coherent all-electrical interface between polar molecules and mesoscopic superconducting resonators. Nat. Phys. 2, 636–642 (2006).

    Google Scholar 

  10. 10.

    DeMille, D., Doyle, J. M. & Sushkov, A. O. Probing the frontiers of particle physics with tabletop-scale experiments. Science 357, 990–994 (2017).

    ADS  CAS  PubMed  Google Scholar 

  11. 11.

    Gregory, P. D., Blackmore, J. A., Bromley, S. L. & Cornish, S. L. Loss of ultracold 87Rb133Cs molecules via optical excitation of long-lived two-body collision complexes. Phys. Rev. Lett. 124, 163402 (2020).

    ADS  CAS  PubMed  Google Scholar 

  12. 12.

    Hu, M. G. et al. Direct observation of bimolecular reactions of ultracold KRb molecules. Science 366, 1111–1115 (2019).

    ADS  CAS  PubMed  Google Scholar 

  13. 13.

    Kirste, M. et al. Quantum-state resolved bimolecular collisions of velocity-controlled OH with NO radicals. Science 338, 1060–1063 (2012).

    ADS  CAS  PubMed  Google Scholar 

  14. 14.

    Christianen, A., Zwierlein, M. W., Groenenboom, G. C. & Karman, T. Photoinduced two-body loss of ultracold molecules. Phys. Rev. Lett. 123, 123402 (2019).

    ADS  CAS  PubMed  Google Scholar 

  15. 15.

    Danzl, J. G. et al. Quantum gas of deeply bound ground state molecules. Science 321, 1062–1066 (2008).

    ADS  CAS  PubMed  Google Scholar 

  16. 16.

    Seeßelberg, F. et al. Extending rotational coherence of interacting polar molecules in a spin-decoupled magic trap. Phys. Rev. Lett. 121, 253401 (2018).

    ADS  PubMed  Google Scholar 

  17. 17.

    Will, S. A., Park, J. W., Yan, Z. Z., Loh, H. & Zwierlein, M. W. Coherent microwave control of ultracold 23Na40K molecules. Phys. Rev. Lett. 116, 225306 (2016).

    ADS  PubMed  Google Scholar 

  18. 18.

    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  CAS  PubMed  Google Scholar 

  19. 19.

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

    CAS  Google Scholar 

  20. 20.

    Anderegg, L. et al. An optical tweezer array of ultracold molecules. Science 365, 1156–1158 (2019).

    ADS  CAS  PubMed  Google Scholar 

  21. 21.

    Ding, S., Wu, Y., Finneran, I. A., Burau, J. J. & Ye, J. Sub-Doppler cooling and compressed trapping of YO molecules at μK temperatures. Phys. Rev. X 10, 021049 (2020).

    CAS  Google Scholar 

  22. 22.

    Yang, H. et al. Observation of magnetically tunable Feshbach resonances in ultracold 23Na40K + 40K collisions. Science 363, 261–264 (2019).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  23. 23.

    Son, H., Park, J. J., Ketterle, W. & Jamison, A. O. Collisional cooling of ultracold molecules. Nature 580, 197–200 (2020).

    ADS  CAS  PubMed  Google Scholar 

  24. 24.

    Segev, Y. et al. Collisions between cold molecules in a superconducting magnetic trap. Nature 572, 189–193 (2019).

    ADS  CAS  PubMed  Google Scholar 

  25. 25.

    Baranov, M. A., Dalmonte, M., Pupillo, G. & Zoller, P. Condensed matter theory of dipolar quantum gases. Chem. Rev. 112, 5012–5061 (2012).

    CAS  PubMed  Google Scholar 

  26. 26.

    Aikawa, K. et al. Reaching Fermi degeneracy via universal dipolar scattering. Phys. Rev. Lett. 112, 010404 (2014).

    ADS  CAS  PubMed  Google Scholar 

  27. 27.

    DeMarco, B. & Jin, D. S. Onset of Fermi degeneracy in a trapped atomic gas. Science 285, 1703–1706 (1999).

    CAS  PubMed  Google Scholar 

  28. 28.

    Quéméner, G. & Bohn, J. L. Dynamics of ultracold molecules in confined geometry and electric field. Phys. Rev. A 83, 012705 (2011).

    ADS  Google Scholar 

  29. 29.

    Micheli, A. et al. Universal rates for reactive ultracold polar molecules in reduced dimensions. Phys. Rev. Lett. 105, 073202 (2010).

    ADS  PubMed  Google Scholar 

  30. 30.

    Zhu, B., Quéméner, G., Rey, A. M. & Holland, M. J. Evaporative cooling of reactive polar molecules confined in a two-dimensional geometry. Phys. Rev. A 88, 063405 (2013).

    ADS  Google Scholar 

  31. 31.

    de Miranda, M. H. G. et al. Controlling the quantum stereodynamics of ultracold bimolecular reactions. Nat. Phys. 7, 502–507 (2011).

    Google Scholar 

  32. 32.

    Covey, J. P. Enhanced Optical and Electric Manipulation of a Quantum Gas of KRb Molecules. Thesis, Univ. Colorado, https://doi.org/10.1007/978-3-319-98107-9 (2018).

  33. 33.

    Shvarchuck, I. et al. Bose–einstein condensation into nonequilibrium states studied by condensate focusing. Phys. Rev. Lett. 89, 270404 (2002).

    CAS  PubMed  Google Scholar 

  34. 34.

    Hueck, K. et al. Two-dimensional homogeneous Fermi gases. Phys. Rev. Lett. 120, 060402 (2018).

    ADS  CAS  PubMed  Google Scholar 

  35. 35.

    Ni, K.-K. et al. A high phase-space-density gas of polar molecules. Science 322, 231–235 (2008).

    ADS  CAS  PubMed  Google Scholar 

  36. 36.

    Quéméner, G. & Bohn, J. L. Strong dependence of ultracold chemical rates on electric dipole moments. Phys. Rev. A 81, 022702 (2010).

    ADS  Google Scholar 

  37. 37.

    Bohn, J. L., Cavagnero, M. & Ticknor, C. Quasi-universal dipolar scattering in cold and ultracold gases. New J. Phys. 11, 055039 (2009).

    ADS  Google Scholar 

  38. 38.

    Ticknor, C. Quasi-two-dimensional dipolar scattering. Phys. Rev. A 81, 042708 (2010).

    ADS  Google Scholar 

  39. 39.

    Bohn, J. L. & Jin, D. S. Differential scattering and rethermalization in ultracold dipolar gases. Phys. Rev. A 89, 022702 (2014).

    ADS  Google Scholar 

  40. 40.

    Aikawa, K. et al. Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of equilibrium. Phys. Rev. Lett. 113, 263201 (2014).

    ADS  CAS  PubMed  Google Scholar 

  41. 41.

    Babadi, M. & Demler, E. Collective excitations of quasi-two-dimensional trapped dipolar fermions: transition from collisionless to hydrodynamic regime. Phys. Rev. A 86, 063638 (2012).

    ADS  Google Scholar 

  42. 42.

    Giorgini, S., Pitaevskii, L. P. & Stringari, S. Theory of ultracold atomic Fermi gases. Rev. Mod. Phys. 80, 1215 (2008).

    ADS  CAS  Google Scholar 

  43. 43.

    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).

    ADS  PubMed  Google Scholar 

  44. 44.

    Góral, K., Santos, L. & Lewenstein, M. Quantum phases of dipolar bosons in optical lattices. Phys. Rev. Lett. 88, 170406 (2002).

    ADS  PubMed  Google Scholar 

  45. 45.

    Capogrosso-Sansone, B., Trefzger, C., Lewenstein, M., Zoller, P. & Pupillo, G. Quantum phases of cold polar molecules in 2D optical lattices. Phys. Rev. Lett. 104, 125301 (2010).

    ADS  CAS  PubMed  Google Scholar 

  46. 46.

    Cooper, N. R. & Shlyapnikov, G. V. Stable topological superfluid phase of ultracold polar fermionic molecules. Phys. Rev. Lett. 103, 155302 (2009).

    ADS  CAS  PubMed  Google Scholar 

  47. 47.

    Gorshkov, A. V. et al. Tunable superfluidity and quantum magnetism with ultracold polar molecules. Phys. Rev. Lett. 107, 115301 (2011).

    ADS  PubMed  Google Scholar 

  48. 48.

    Potter, A. C., Berg, E., Wang, D. W., Halperin, B. I. & Demler, E. Superfluidity and dimerization in a multilayered system of fermionic polar molecules. Phys. Rev. Lett. 105, 220406 (2010).

    ADS  PubMed  Google Scholar 

  49. 49.

    Yao, N. Y. et al. Many-body localization in dipolar systems. Phys. Rev. Lett. 113, 243002 (2014).

    ADS  CAS  PubMed  Google Scholar 

  50. 50.

    Barbiero, L., Menotti, C., Recati, A. & Santos, L. Out-of-equilibrium states and quasi-many-body localization in polar lattice gases. Phys. Rev. B 92, 180406 (2015).

    ADS  Google Scholar 

  51. 51.

    Zinner, N. T. & Bruun, G. M. Density waves in layered systems with fermionic polar molecules. Eur. Phys. J. D 65, 133–139 (2011).

    ADS  CAS  Google Scholar 

  52. 52.

    Peter, D., Müller, S., Wessel, S. & Büchler, H. P. Anomalous behavior of spin systems with dipolar interactions. Phys. Rev. Lett. 109, 025303 (2012).

    ADS  CAS  PubMed  Google Scholar 

  53. 53.

    Dalfovo, F., Giorgini, S., Pitaevskii, L. P. & Stringari, S. Theory of Bose–Einstein condensation in trapped gases. Rev. Mod. Phys. 71, 463–512 (1999).

    ADS  CAS  Google Scholar 

  54. 54.

    Inguscio, M., Ketterle, W. & Salomon, C. Ultra-cold Fermi gases. In Proceedings of the International School of Physics ‘Enrico Fermi’ (2007).

Download references

Acknowledgements

We acknowledge funding from NIST, DARPA DRINQS, ARO MURI and NSF Phys-1734006. We thank J. L. Bohn, A. M. Kaufman, and C. Miller for careful reading of the manuscript and T. Brown for technical assistance.

Author information

Affiliations

Authors

Contributions

All authors contributed to carrying out the experiments, interpreting the results, and writing the manuscript.

Corresponding authors

Correspondence to Giacomo Valtolina or Jun Ye.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Georgy Shlyapnikov and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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

Extended data figures and tables

Extended Data Fig. 1 Layer occupancy.

Histogram of the average number per layer (relative population) for the data shown in Fig. 1c.

Extended Data Fig. 2 Trend of ωx/(2π) versus γ.

Grey points are the experimental measurements at EDC = 5 kV cm−1, the solid grey line is a linear fit to guide the eye, and the dashed line is the prediction (Sim) from the finite-element model. All error bars are 1 standard deviation of the mean.

Extended Data Fig. 3 Evaporation sequence.

a, Ramp in EDC. b, Ramp in γ. c, Trap depth versus time from the finite-element model of electro-optical potential. d, Evolution of η, calculated by taking the ratio of the trap depth and temperature at each time point. e, Evolution of T/TF during the ramp. All error bars are 1 standard error of the mean.

Extended Data Fig. 4 Fermi gas thermometry.

Trend of Tout/Trel as a function of the excluded region from the centre of the Gaussian fit for T/TF = 0.81(15) (orange diamonds) and T/TF = 2.0(1) (black circles). Solid lines are Gaussian fits to simulated density profiles for T/TF = 2.0 (black) and T/TF = 0.8 (orange). All error bars are 1 standard error of the mean.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Valtolina, G., Matsuda, K., Tobias, W.G. et al. Dipolar evaporation of reactive molecules to below the Fermi temperature. Nature 588, 239–243 (2020). https://doi.org/10.1038/s41586-020-2980-7

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links