HOME / RESEARCH /

CaOH - Ultracold Triatomic Molecules

Research Overview

SrOHThe goal of this experiment is to bring polyatomic molecules into the ultracold regime using direct laser cooling. The use of laser radiation to control and cool external and internal degrees of freedom has revolutionized atomic, molecular, and optical physics [1]. The powerful techniques of laser cooling and trapping using light scattering forces for atoms led to breakthroughs in both fundamental and applied sciences, including detailed studies of degenerate quantum gases and many-body physics [2,3], creation of novel frequency standards [4], and precision measurements of fundamental constants [5,6]. Polyatomic molecules are more difficult to manipulate than atoms and diatomic molecules because they possess additional rotational and vibrational degrees of freedom. Partially because of their increased complexity, cold dense samples of molecules with three or more atoms offer unique capabilities for exploring interdisciplinary frontiers in physics, chemistry and even biology. Precise control over polyatomic molecules could lead to applications in astrophysics [7], quantum simulation [8] and computation [9,10], fundamental physics [11,12], and chemistry [13]. Study of parity violation in biomolecular chirality [14]—which plays a fundamental role in molecular biology [15]—necessarily requires polyatomic molecules.

Motivated by recent successes in the laser cooling and trapping of diatomic molecules [16-20], as well as recent demonstrations in our group of laser cooling of triatomic molecules [21-24], we are currently working to load a magneto-optical trap (MOT) with the linear, triatomic molecule calcium monohydroxide (CaOH). Our approach starts with buffer gas cooling [25-27], a technique that dramatically reduces the number of populated internal rotational and vibrational states by thermalizing a sample of molecules with helium gas at ~2K. This initial cooling step is critical for working with molecules to limit the number of quantum states that have significant population, and our two-stage buffer gas cell design has additionally allowed us to produce a slow beam of CaOH molecules with a peak velocity below 100 m/s. We are now working to adapt successful atomic and diatomic laser cooling techniques to triatomic CaOH. We have recently demonstrated 1D cooling and compression of the molecular beam using a one-dimensional MOT [28]; this has allowed us to demonstrate the feasibility of scattering thousands of photons via radiative cooling and the application of magneto-optical forces, both of which will be necessary for 3D trapping. We will next radiatively slow the CaOH beam, which can be accomplished using a white-light slowing scheme [29]. We will then produce a 3D MOT using techniques similar to those demonstrated with diatomic SrF and CaF [16-18]. Unlike electronic and rotational transitions, there are no selection rules governing vibrational degrees of freedom in molecules, forcing us to rely on molecule-dependent vibrational branching ratios to avoid decay out of the cooling cycle. These have been shown to be favorable in CaOH [30], meaning that direct laser cooling and slowing should be feasible with a manageable number of repumping lasers.

We are additionally examining how to extend laser cooling techniques to more complex polyatomic molecules, such as symmetric tops like CaOCH3, and have identified a number of large polyatomics expected to have near-diagonal Franck-Condon factors [30, 31].

 

Latest News

November 2023: We have sucessfully loaded CaOH molecules into an optical tweezer array. Read about our newest results on arXiv here.
April 2024 update: These results have now been published in Nature.

CaOH Tweezer Array

January 2023: Our latest work on "Quantum Control of Trapped Polyatomic Molecules for eEDM Searches" is now on arXiv. This work has been published on Science. 

Spin precession

August 2022: We have sub-Doppler cooled and trapped CaOH molecules in an optical dipole trap, and measured the lifetime of an excited vibrational bending mode. See the results on the arXiv here: "Optical Trapping of a Polyatomic Molecule in an l-Type Parity Doublet State". This work has been accepted for publication in Physical Review Letters.

CaOH ODT

DecCaOH MOTember 2021: We realized a MOT of CaOH molecules. See the results on the arXiv here. Our results have now been published in Nature, see "Magneto-optical trapping and sub-Doppler cooling of a polyatomic molecule".​

 

Our results on "Direct Laser Cooling of a Symmetric Top Molecule"  have been published in Science. Also see the accompanying Perspective, "Laser cooling of larger quantum objects."

caoch3_figure

Our results on "Establishing a nearly closed cycling transition in a polyatomic molecule"  have been published in PRA. These results clear the path for radiative slowing and trapping CaOH in a MOT.

scheme_v2

Our first CaOH results on “1D Magneto-Optical Trap of Polyatomic Molecules” have been published in Phys Rev. Lett. as an Editor's Suggestion. arXiv: 2001.10525

caoh_1d_mot

Our results on “Coherent bichromatic force deflection of molecules” have been published in PRL as an Editor’s Suggestion.SrOH and BCF fieldsOur results on “Sisyphus laser cooling of a polyatomic molecule” have been published in PRL as an Editor’s Suggestion and Featured in Physics. See the accompanying viewpoint article “A diatomic molecules is one atom too few”.

Sisyphus

 

References

  1. Phillips Rev. Mod. Phys. 70, 721 (1998)

  2. Bloch et al. Rev. Mod. Phys. 80, 885 (2008)

  3. Mazurenko et al. Nature 545, 462 (2017)

  4. Ludlow et al. Rev. Mod. Phys. 87, 637 (2015)

  5. Fixler et al. Science 315 74 (2007)

  6. Cladé et al. Phys. Rev. Lett. 96 033001 (2006)

  7. Herbst et al. Annu. Rev. Astron. Astrophys. 47 427 (2009)

  8. Wall et al. New J. Phys. 17 025001 (2015)

  9. Tesch et al. Phys. Rev. Lett. 89 157901 (2002)

  10. Yu et al. New J. Phys. 21 093049 (2019)

  11. Kozlov Phys. Rev. A 87 032104 (2013)

  12. Kozlov et al. Ann. Phys. 525 452 2013

  13. Sabbah et al. Science 317 102 (2007)

  14. Quack et al. Annu. Rev. Phys. Chem. 59 741 (2008)

  15. Quack Angew. Chem. Int. Ed. 41 4618 (2002)

  16. Barry et al. Nature 512, 286 (2014)

  17. Truppe et al. Nature Phys. 13, 1173 (2017)

  18. Anderegg et al. Phys. Rev. Lett. 119, 103201 (2017)

  19. Anderegg et al. Nature Phys. 14, 890 (2018)

  20. Cheuk et al. Phys. Rev. Lett. 121, 083201 (2018)

  21. Kozyryev et al. J. Phys. B 49, 134002 (2016)

  22. Kozyryev et al. Phys. Rev. Lett. 118, 173201 (2017)

  23. Kozyryev et al. Phys. Rev. Lett. 120, 063205 (2018)

  24. Augenbraun et al. New J. Phys. (2020)

  25. Hutzler et al. Chem. Rev., 112, 4803 (2012)

  26. Lu et al. Phys. Chem. Chem. Phys. 13, 18986 (2011)

  27. Patterson et al. J. Chem. Phys. 126, 154307 (2007)

  28. Baum et al. Phys. Rev. Lett.124, 133201 (2020)

  29. Hemmerling et al. J. Phys. B 49, 174001 (2016)

  30. Kozyryev et al. New J. Phys. 21, 052002 (2019)
  31. Kozyryev et al. ChemPhysChem 17, 3641 (2016)