Laser Cooling, Optical Trapping, and Quantum Control of Polyatomic Molecules

Abstract

Polyatomic molecules contain diverse structures – including rotational and vibrational degrees of freedom, nuclear and electronic spins, and electric dipole moments – that make them promising for a range of quantum science applications. These include quantum information science, quantum simulation, studies of ultracold collisions and ultracold chemistry, and precision searches for physics beyond the Standard Model. However, maximizing the potential of polyatomic molecules for these applications requires them to be cooled to ultracold temperatures ( mK), trapped in three dimensions, and controlled at the single quantum state level. Significant progress has been made with diatomic molecules over the last fifteen years, but the increased complexity of polyatomic species (defined as molecules containing more than two atoms) makes them more challenging to control at the same level. In this thesis, we describe our work bringing a linear triatomic molecule, calcium monohydroxide (CaOH), into the quantum regime. We demonstrate laser cooling of CaOH molecules to microkelvin temperatures, confinement in a magneto-optical trap (MOT), and loading of conservative optical dipole traps and optical tweezer arrays. We characterize the lifetime of low-lying vibrational states of CaOH in optical traps, including the vibrational bending mode, whose parity-doublet states are a key resource for many applications. Next, we develop techniques for preparing CaOH molecules in a single internal quantum state and for coherently manipulating the internal state with microwave and radio-frequency fields. We also show that we can nondestructively and state-selectively detect trapped CaOH molecules, including single molecules in optical tweezers. We demonstrate the applicability of these tools to applications including precision measurements, quantum information science, and ultracold collisions. We establish a method for future CP-violating physics searches with optically trapped polyatomic molecules, by identifying states that are sensitive to the electron electric dipole moment (eEDM) and showing that these states have long coherence times in CaOH. We identify potential qubit states in the CaOH bending mode and show that they can be coherently controlled at the single-molecule level in an optical tweezer array. Finally, we observe and characterize single quantum-state-controlled collisions between ultracold CaOH molecules, and identify states in the bending mode that could potentially be used for evaporative cooling to quantum degeneracy. Compared to linear triatomic molecules, nonlinear molecules contain even more structures that can be harnessed for quantum science applications, at the cost of making them even more challenging to cool and control. Towards this goal, in this thesis we describe work demonstrating 1D laser cooling of a beam of CaOCH3, a symmetric top molecule. This contributes to a growing body of evidence that complex polyatomic molecules could soon be cooled, trapped, and controlled at ultracold temperatures.