Since the original work on Bose–Einstein condensation1,2, the use of quantum degenerate gases of atoms has enabled the quantum emulation of important systems in condensed matter and nuclear physics, as well as the study of many-body states that have no analogue in other fields of physics3. Ultracold molecules in the micro- and nanokelvin regimes are expected to bring powerful capabilities to quantum emulation4 and quantum computing5, owing to their rich internal degrees of freedom compared to atoms, and to facilitate precision measurement and the study of quantum chemistry6. Quantum gases of ultracold atoms can be created using collision-based cooling schemes such as evaporative cooling, but thermalization and collisional cooling have not yet been realized for ultracold molecules. Other techniques, such as the use of supersonic jets and cryogenic buffer gases, have reached temperatures limited to above 10 millikelvin7,8. Here we show cooling of NaLi molecules to micro- and nanokelvin temperatures through collisions with ultracold Na atoms, with both molecules and atoms prepared in their stretched hyperfine spin states. We find a lower bound on the ratio of elastic to inelastic molecule–atom collisions that is greater than 50—large enough to support sustained collisional cooling. By employing two stages of evaporation, we increase the phase-space density of the molecules by a factor of 20, achieving temperatures as low as 220 nanokelvin. The favourable collisional properties of the Na–NaLi system could enable the creation of deeply quantum degenerate dipolar molecules and raises the possibility of using stretched spin states in the cooling of other molecules.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
Nature Open Access 27 July 2022
Subscribe to Nature+
Get immediate online access to Nature and 55 other Nature journal
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Anderson, M. H., Ensher, J. R., Matthews, M. R., Wieman, C. E. & Cornell, E. A. Observation of Bose–Einstein condensation in a dilute atomic vapor. Science 269, 198–201 (1995).
Davis, K. B. et al. Bose–Einstein condensation in a gas of sodium atoms. Phys. Rev. Lett. 75, 3969–3973 (1995).
Bloch, I., Dalibard, J. & Zwerger, W. Many-body physics with ultracold gases. Rev. Mod. Phys. 80, 885–964 (2008).
Baranov, M. A., Dalmonte, M., Pupillo, G. & Zoller, P. Condensed matter theory of dipolar quantum gases. Chem. Rev. 112, 5012–5061 (2012).
DeMille, D. Quantum computation with trapped polar molecules. Phys. Rev. Lett. 88, 067901 (2002).
Carr, L. D., DeMille, D., Krems, R. V. & Ye, J. Cold and ultracold molecules: science, technology and applications. New J. Phys. 11, 055049 (2009).
Christen, W., Rademann, K. & Even, U. Efficient cooling in supersonic jet expansions of supercritical fluids: CO and CO2. J. Chem. Phys. 125, 174307 (2006).
Weinstein, J. D., deCarvalho, R., Guillet, T., Friedrich, B. & Doyle, J. M. Magnetic trapping of calcium monohydride molecules at millikelvin temperatures. Nature 395, 148–150 (1998).
Stellmer, S., Pasquiou, B., Grimm, R. & Schreck, F. Laser cooling to quantum degeneracy. Phys. Rev. Lett. 110, 263003 (2013).
Hu, J. et al. Creation of a Bose-condensed gas of 87Rb by laser cooling. Science 358, 1078–1080 (2017).
Soldán, P. & Hutson, J. M. Interaction of NH(X 3Σ−) molecules with rubidium atoms: implications for sympathetic cooling and the formation of extremely polar molecules. Phys. Rev. Lett. 92, 163202 (2004).
Elioff, M. S., Valentini, J. J. & Chandler, D. W. Subkelvin cooling NO molecules via ‘billiard-like’ collisions with argon. Science 302, 1940–1943 (2003).
Henson, A. B., Gersten, S., Shagam, Y., Narevicius, J. & Narevicius, E. Observation of resonances in Penning ionization reactions at sub-kelvin temperatures in merged beams. Science 338, 234–238 (2012).
Tokunaga, S. K. et al. Prospects for sympathetic cooling of molecules in electrostatic, a.c. and microwave traps. Eur. Phys. J. D 65, 141–149 (2011)
González-Martínez, M. L. & Hutson, J. M. Ultracold hydrogen atoms: a versatile coolant to produce ultracold molecules. Phys. Rev. Lett. 111, 203004 (2013).
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).
Morita, M., Kosicki, M. B. Z., Żuchowski, P. S. & Tscherbul, T. V. Atom–molecule collisions, spin relaxation, and sympathetic cooling in an ultracold spin-polarized Rb(2S)−SrF(2Σ+) mixture. Phys. Rev. A 98, 042702 (2018).
Augustovčová, L. D. & Bohn, J. Ultracold collisions of polyatomic molecules: CaOH. New J. Phys. 21, 103022 (2019).
Segev, Y. et al. Collisions between cold molecules in a superconducting magnetic trap. Nature 572, 189–193 (2019).
Reens, D., Wu, H., Langen, T. & Ye, J. Controlling spin flips of molecules in an electromagnetic trap. Phys. Rev. A 96, 063420 (2017).
Stuhl, B. K. et al. Evaporative cooling of the dipolar hydroxyl radical. Nature 492, 396–400 (2012).
Ni, K.-K. et al. A high phase-space-density gas of polar molecules. Science 322, 231–235 (2008).
Barry, J. F., McCarron, D. J., Norrgard, E. B., Steinecker, M. H. & DeMille, D. Magneto-optical trapping of a diatomic molecule. Nature 512, 286 (2014).
Anderegg, L. et al. Radio frequency magneto-optical trapping of CaF with high density. Phys. Rev. Lett. 119, 103201 (2017).
Truppe, S. et al. Molecules cooled below the doppler limit. Nat. Phys. 13, 1173–1176 (2017).
Collopy, A. L. et al. 3-D magneto-optical trap of yttrium monoxide. Phys. Rev. Lett. 121, 213201 (2018).
Żuchowski, Z. P. S. & Hutson, J. M. Reactions of ultracold alkali-metal dimers. Phys. Rev. A 81, 060703 (2010).
Mayle, M., Quéméner, G., Ruzic, B. P. & Bohn, J. L. Scattering of ultracold molecules in the highly resonant regime. Phys. Rev. A 87, 012709 (2013).
Christianen, A., Zwierlein, M. W., Groenenboom, G. C. & Karman, T. Trapping laser excitation during collisions limits the lifetime of ultracold molecules. Phys. Rev. Lett. 123, 123402 (2019).
Myatt, C. J., Burt, E. A., Ghrist, R. W., Cornell, E. A. & Wieman, C. E. Production of two overlapping Bose–Einstein condensates by sympathetic cooling. Phys. Rev. Lett. 78, 586–589 (1997).
Janssen, L. M. C., van der Avoird, A. & Groenenboom, G. C. Quantum reactive scattering of ultracold NH(X 3Σ −) radicals in a magnetic trap. Phys. Rev. Lett. 110, 063201 (2013).
Krems, R. V. & Dalgarno, A. Quantum-mechanical theory of atom–molecule and molecular collisions in a magnetic field: spin depolarization. J. Chem. Phys. 120, 2296–2307 (2004).
Żuchowski, P. S. & Hutson, J. M. Cold collisions of N(4S) atoms and NH(3Σ) molecules in magnetic fields. Phys. Chem. Chem. Phys. 13, 3669–3680 (2011).
Tscherbul, T. V., Kłos, J. & Buchachenko, A. A. Ultracold spin-polarized mixtures of 2Σ molecules with s-state atoms: collisional stability and implications for sympathetic cooling. Phys. Rev. A 84, 040701 (2011).
Rvachov, T. M. et al. Long-lived ultracold molecules with electric and magnetic dipole moments. Phys. Rev. Lett. 119, 143001 (2017).
Heo, M.-S. et al. Formation of ultracold fermionic NaLi Feshbach molecules. Phys. Rev. A 86, 021602 (2012).
Idziaszek, Z. & Julienne, P. S. Universal rate constants for reactive collisions of ultracold molecules. Phys. Rev. Lett. 104, 113202 (2010).
Hummon, M. T. et al. Cold N + NH collisions in a magnetic trap. Phys. Rev. Lett. 106, 053201 (2011).
Campbell, W. C. et al. Mechanism of collisional spin relaxation in 3Σ molecules. Phys. Rev. Lett. 102, 013003 (2009).
Warehime, M. & Kłos, J. Nonadiabatic collisions of CaH with Li: importance of spin–orbit-induced spin relaxation in spin-polarized sympathetic cooling of CaH. Phys. Rev. A 92, 032703 (2015).
Hadzibabic, Z. et al. Fiftyfold improvement in the number of quantum degenerate fermionic atoms. Phys. Rev. Lett. 91, 160401 (2003).
Mosk, A. et al. Mixture of ultracold lithium and cesium atoms in an optical dipole trap. Appl. Phys. B 73, 791–799 (2001).
Ivanov, V. V. et al. Sympathetic cooling in an optically trapped mixture of alkali and spin-singlet atoms. Phys. Rev. Lett. 106, 153201 (2011).
Lang, F., Winkler, K., Strauss, C., Grimm, R. & Denschlag, J. H. Ultracold triplet molecules in the rovibrational ground state. Phys. Rev. Lett. 101, 133005 (2008).
Danzl, J. G. et al. An ultracold high-density sample of rovibronic ground-state molecules in an optical lattice. Nat. Phys. 6, 265 (2010).
Takekoshi, T. et al. Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state. Phys. Rev. Lett. 113, 205301 (2014).
Molony, P. K. et al. Creation of ultracold 87Rb133Cs molecules in the rovibrational ground state. Phys. Rev. Lett. 113, 255301 (2014).
Park, J. W., Will, S. A. & Zwierlein, M. W. Ultracold dipolar gas of fermionic 23Na40K molecules in their absolute ground state. Phys. Rev. Lett. 114, 205302 (2015).
Guo, M. et al. Creation of an ultracold gas of ground-state dipolar 23Na87Rb molecules. Phys. Rev. Lett. 116, 205303 (2016).
Yang, H. et al. Observation of magnetically tunable Feshbach resonances in ultracold 23Na40K + 40K collisions. Science 363, 261–264 (2019).
Seeßelberg, F. et al. Extending rotational coherence of interacting polar molecules in a spin-decoupled magic trap. Phys. Rev. Lett. 121, 253401 (2018).
Rvachov, T. M. et al. Photoassociation of ultracold NaLi. Phys. Chem. Chem. Phys. 20, 4746–4751 (2018).
Rvachov, T. M. et al. Two-photon spectroscopy of the NaLi triplet ground state. Phys. Chem. Chem. Phys. 20, 4739–4745 (2018).
Cook, E. C., Martin, P. J., Brown-Heft, T. L., Garman, J. C. & Steck, D. A. High passive-stability diode-laser design for use in atomic-physics experiments. Rev. Sci. Instrum. 83, 043101 (2012).
Mukaiyama, T., Abo-Shaeer, J. R., Xu, K., Chin, J. K. & Ketterle, W. Dissociation and decay of ultracold sodium molecules. Phys. Rev. Lett. 92, 180402 (2004).
Ravensbergen, C. et al. Production of a degenerate Fermi–Fermi mixture of dysprosium and potassium atoms. Phys. Rev. A 98, 063624 (2018).
Derevianko, A., Babb, J. F. & Dalgarno, A. High-precision calculations of van der Waals coefficients for heteronuclear alkali-metal dimers. Phys. Rev. A 63, 052704 (2001).
We thank M. Zwierlein for discussions and J. Yao for technical assistance. We acknowledge support from the NSF through the Center for Ultracold Atoms and award 1506369, from the NASA Fundamental Physics Program and from the Samsung Scholarship.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Son, H., Park, J.J., Ketterle, W. et al. Collisional cooling of ultracold molecules. Nature 580, 197–200 (2020). https://doi.org/10.1038/s41586-020-2141-z
This article is cited by
Frontiers of Physics (2022)
Nature Physics (2021)
Nature Reviews Chemistry (2021)