Session U03: Laser-cooled Molecules for Precision Measurement

Precision Measurement with Polyatomic Molecules

Polyatomic molecule uniquely enable the simultaneous combination of multiple features advantageous for precision measurement. Searches for charge-parity (CP) violation benefit from large internal molecular fields, high polarizability, internal co-magnetometry, and the ability to cycle photons - all of which can be found in certain polyatomic species. We discuss experimental and theoretical developments in several linear metal hydroxide (MOH) species. These include spectroscopic mapping of EDM-sensitive states, new spectroscopic methods for transitions relevant to laser cooling, photon cycling in species with complex hyperfine structure, and the demonstration of a "pathfinder" EDM experiment with ultracold and trapped polyatomics. We discuss how polyatomic structure gives rise to unique capabilities, such as the existince of EDM-sensitive yet field-insensitive measurement schemes. We also discuss progress towards extending these methods to species with short-lived nuclei, more complex ligands, and other advantageous features for precision measurement.   

Laser cooling of barium monofluoride molecules

I will report on our progress towards laser cooling of barium monofluoride molecules. Due to its high mass, resolved hyperfine structure in the excited state and branching losses through intermediate states, this molecular species is notoriously difficult to cool, but it shows high promise for various types of precision measurement applications. I will discuss laser cooling strategies for both the bosonic isotopologues, which are interesting for electron EDM searches, and the more complex fermionic isotopologues, which are used for parity violation experiments.   

Progress toward an ultracold trap of SrOH molecules to probe fundamental constant variations and the electron electric dipole moment

We present experimental progress towards laser slowing and trapping of SrOH molecules. The long coherence times possible in a trapped, ultracold sample will enable two complementary searches for beyond-the-Standard-Model physics. First, because vibrational and rotational energies of molecules generically depend on the proton-to-electron mass ratio, μ, certain dark matter models that induce oscillations in μ can be probed via precision spectroscopy of rovibrational transitions. A low-lying accidental near-degeneracy between stretching and bending vibrational states in SrOH can be probed with experimentally convenient microwave transitions. Second, the nearly-degenerate opposite-parity states of the bending vibrational mode provide access to the moderate effective electric field of 2 GV/cm at small externally applied fields, and also serve as co-magnetometer states. Combined with the long coherence times and large numbers possible in a trap of ultracold SrOH molecules, we anticipate competitive sensitivity to the electron electric dipole moment. We describe recent developments of the experimental apparatus, including a new cryogenic buffer gas beam source, the full laser slowing and cooling system comprised of 10 sum-frequency-generated lasers, and work toward 2D transverse cooling for increased loading efficiency into a magneto-optical trap.   

Towards an infrared frequency standard using CaF molecules in a lattice

Clock comparisons provide exceptionally precise constraints on present day variations of the fine structure constant (α) and the electron-to-proton mass ratio (m_e/m_p) [1]. These measurements constrain the parameter spaces of ultralight dark matter models and probe models of Lorentz violation, dark energy, grand unification theories and quantum gravity [2]. By comparing a molecular vibrational frequency to an optical atomic clock, it seems possible to make improved measurements of the variations of m_e/m_p. Moreover, vibrational frequency measurements can serve as frequency standards in the infrared, a region of the spectrum where current standards are poor. We propose a molecular clock based on the 17 μm fundamental vibrational transition of ultracold CaF molecules in an optical lattice. We calculate the differential ac polarizability of the vibrational states and find several convenient magic wavelengths where the clock transition is insensitive to the lattice intensity. We show that the transition has low sensitivity to electric fields, magnetic fields and blackbody radiation and project that a fractional inaccuracy below 10^-17 is feasible. We will report our progress on cooling molecules into an optical lattice, developing a 17 μm laser system to drive the vibrational transition directly, and developing a Raman laser system for the clock.

[1] R. Lange et al, Phys. Rev. Lett 126, 011102 (2021).

[2] G. Barontini et al, EPJ Quantum Technology 9, 12 (2022).