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Quantum-State-Controlled Collisions of Ultracold Polyatomic Molecules

Nathaniel B. Vilas1,2,*,†, Paige Robichaud1,2, Christian Hallas1,2, Junheng Tao1,2, Loïc Anderegg1,2,‡, Grace K. Li1,2, Hana Lampson1,2, Lucie D. Augustovičová3, John L. Bohn4 et al.

John M. Doyle1,2

  • *Contact author: vilas@g.harvard.edu
  • †Present address: Department of Physics, University of California, Berkeley, California 94720, USA.
  • ‡Present address: Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA.
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Phys. Rev. X 16, 021001 – Published 1 April, 2026

DOI: https://doi.org/10.1103/w1jn-h3sv

Abstract

Collisions between ultracold calcium monohydroxide (CaOH) molecules are realized and studied. Inelastic collision rate constants are measured for CaOH prepared in ground and excited vibrational states, and the electric field dependence of these rates is measured for molecules in single quantum states of the parity-doubled bending mode. Theoretical calculations of collision rate coefficients are performed and found to agree with measured values. The lowest collisional loss rates are for states with repulsive long-range potentials that shield ultracold molecules from loss channels at short distance. These results unveil the collisional behavior of parity-doublet molecules in the ultracold regime and lay the foundation for future experiments to evaporatively cool polyatomic molecules to quantum degeneracy.

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Polyatomic Molecules Get Two Steps Closer to Quantum Horizon

Published 1 April, 2026

Researchers have improved trapping of polyatomic molecules while also controlling their collisions—two important advances for ultracold polyatomic molecular physics.

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Popular Summary

Understanding and controlling the collisions of polyatomic molecules at temperatures below 1 mK is essential for applications ranging from quantum simulation to precision tests of fundamental physics. We observe and characterize collisions between calcium monohydroxide (CaOH) molecules at 100  μK by measuring inelastic loss rates across various internal states and applied electric fields. We find that our results agree well with theoretical calculations based on a universal loss model, which simplifies the complex short-range behavior of molecular collisions. By leveraging the parity-doublet structure present in all polyatomic species, we identify specific quantum states with repulsive long-range potentials that effectively shield the molecules from short-range loss. This shielding could enable the future use of electrostatic methods to evaporatively cool polyatomic molecules to quantum degeneracy. These findings provide a foundation for understanding the collisional behavior of complex molecules at ultracold temperatures, facilitating new frontiers in ultracold chemistry and quantum science.

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Phys. Rev. X 16, 021001– Published 1 April, 2026
  • Received 9 June 2025
  • Revised 19 September 2025
  • Accepted 23 December 2025
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