Researchers Demonstrate Optical Cycling in Thorium Monoxide for Improved Fundamental Physics Tests
Researchers have demonstrated the first optical cycling on thorium monoxide (ThO), a molecule used in leading searches for the electron electric dipole moment (eEDM). ThO does not belong to the conventional alkali-like or alkaline-earth-like molecular classes on which optical cycling has previously been achieved. The advance could more than double the statistical sensitivity of eEDM experiments, which probe fundamental symmetry violations beyond the Standard Model.
A research team has achieved optical cycling on thorium monoxide (ThO) for the first time, demonstrating repeated photon scattering on an electronic transition in a molecule that falls outside the conventional classes where this technique has been established. The experiment showed that both the J=1 and J=2 rotational levels of ThO can scatter approximately 11 photons on average using a single laser, at scattering rates near 2 million per second, before population leaks to other vibronic levels. The team explored a range of experimental parameters including laser intensity, polarization switching rate, and interaction time. They outline a scheme to apply this cycling to ACME-style eEDM measurements, projecting a fourfold improvement in detection efficiency over standard fluorescence detection and a greater than twofold enhancement in statistical sensitivity. The technique is also extensible to scatter roughly 100 photons, which would open the door to broader quantum control and sensing applications using ThO. The eEDM is a key observable in tests of CP symmetry violation and physics beyond the Standard Model, making improved measurement sensitivity scientifically significant.
What's missing
The paper reports a preprint result that has not yet undergone formal peer review. The demonstrated photon scatter count (~11 photons) is well below the ~100-photon target needed for full quantum control applications; the pathway to that extended regime relies on additional repumping lasers whose feasibility is outlined but not yet experimentally demonstrated. The projected sensitivity improvements assume integration into an ACME-style apparatus, and actual gains will depend on systematic noise sources not fully characterized here.
What different sources said
- arXiv physicsCenter
Photon Cycling and Laser Cooling of an Asymmetric Top Molecule
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