Laser-cooled molecules for quantum science and ultracold chemistry

John M. Doyle

Yury Suleymanov

Ultracold Physics Experimental progress over the past few decades has led to the mastery of ultracold atomic gases. A major thrust of current research is to extend this success to ultracold molecules, which would open qualitatively new perspectives for quantum information science, precision measurement, quantum chemistry, and other fields. The internal degrees of freedom in molecules preclude immediate implementation of conventional methods. Using a specific combination of rovibronic optical transitions, Mitra et al. report direct Sisyphus laser cooling of the symmetric top molecule CaOCH3 to temperatures below 1 millikelvin (see the Perspective by Hudson). The proposed scheme for cooling is potentially applicable to a wide range of nonlinear polyatomic molecules. Science , this issue p. [1366][1]; see also p. [1304][2] [1]: /lookup/doi/10.1126/science.abc5357 [2]: /lookup/doi/10.1126/science.abd1657

Noah J. Fitch, Michael R. Tarbutt

Christian Hallas

Ultracold molecules are a promising platform for a wide range of applications in quantum science, including searches for new particles (beyond the Standard Model), quantum computing and simulation, and studies of ultracold collisions and chemistry. Over the last decade, tremendous progress has been made in developing techniques to trap diatomic molecules (molecules containing only two atoms) and cool them to ultracold temperatures using laser cooling. Polyatomic molecules (molecules containing more than two atoms) provide new, unique scientific opportunities not afforded by their diatomic counterparts and represent the next frontier in laser cooling and quantum science with molecules. In this thesis, we present our work on extending laser cooling and quantum control to polyatomic molecules. We describe our demonstration of laser cooling and the creation of a magneto-optical trap (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). We further demonstrate loading of the trapped molecules into an optical dipole trap (ODT) and loading of individual CaOH molecules into the conservative potential an optical tweezer array. We also describe our realization of a new type of MOT developed for molecules, a "conveyor belt MOT", which provides increased compression compared to traditional molecular MOTs and was discovered using numerical simulations of the CaOH MOT that were developed as part of this thesis. The increased MOT density and ODT loading afforded by the conveyor belt MOT provides the density required to perform studies of collisions between ultracold CaOH molecules. We also describe our work on the laser cooling the symmetric top molecule CaOCH₃, opening the possibility for 3-D laser cooling of even larger, more complex molecules into the ultracold regime. With the ability to laser cool and trap CaOH molecules, our most recent work has focused on developing tools for quantum control and on initial explorations of some of the new features afforded by polyatomic molecules. We describe a novel protocol established to perform a measurement of the electron's electric dipole moment ("eEDM"). Looking towards quantum information processing with polyatomic molecules, we create a new type of qubit using parity-doublet states in the bending mode of CaOH and characterize its coherence properties. Finally, we provide a brief outlook towards the future of laser cooling of polyatomic molecules for quantum science and provide a few suggestions for new directions opened up by the work presented in this thesis.

Johanna L. Miller

C. Gabbanini, A. Fioretti