Session K02: Gas-Phase Polyatomic Molecules in Quantum Applications

Quantum Scattering of Fullerene C60 with Rare Gas Atoms

The discovery of fullerene C₆₀ opened new horizons in multidisciplinary scientific research. Designing new fullerene-based materials with specific targeted electronic structures, transport and optical properties remains an exciting challenge in these fields. For example, endohedral C₆₀ was proposed to be natural candidates for functional quantum architectures to store and manipulate atomic and molecular qubits [1]. Recently, single quantum state preparation and control has been achieved in high-resolution spectroscopy of gas-phase C₆₀ molecules, which showed their unusual spectrum of rotational levels associated with the symmetry-induced restrictions on the molecular motion [2]. 

The primary goal of the current research is to create a fully quantitative, quantum description of the C₆₀ molecule. A key part of our theoretical study is the understanding of collisional processes of C₆₀ with a buffer-gas of Ar and He atoms, including an analysis of the electronic structure of these complexes, their interaction anisotropy, and the collision-induced rotational and vibrational quenching of C₆₀. In this work, we emphasize the role of the icosahedral symmetry of C₆₀ on its collisional dynamics as potentially transformative feature for molecular spectroscopy. We have shown, for the first time, that scattering quenching times of highly rotational levels of the C₆₀ vibrational ground state are orders of magnitude longer than those that for molecules of lower symmetry.  In addition, using the icosahedral symmetry group we predict new optical selection rules. 

[1] W. Harneit, Spin Quantum Computing with Endohedral Fullerenes,  in “Endohedral Fullerenes: Electron Transfer and Spin”, (Springer , Ed. A. Popov).

[2] B. Changala, M. L. Weichman, K. F. Lee, M. E. Fermann, Jun Ye,  Science 363, 49-54 (2019).   

Fully controlled individual diatomic polar molecules for quantum science

We have achieved full internal and external quantum state control of an array of 5 molecules in optical tweezers. We pursue to leverage the large (4.6 Debye) dipole moment to interact and to entangle individually trapped NaCs molecules separated by microns. I will report our most recent progress.   

Cold collisions between trapped polyatomic molecules

Understanding the world around us requires understanding molecules and their interaction with other molecules at the most fundamental quantum level. Towards this goal, radically new cooling and trapping techniques have been developed for molecules which cannot straightforwardly be manipulated with lasers. Exploiting the presence of a permanent electric dipole moment especially of polyatomic molecules, the new techniques include electrostatic skimming, guiding and trapping, as well as centrifuge deceleration, cryogenic buffer-gas and Sisyphus cooling. With these techniques implemented in one setting for the first time, we now prepare samples of simultaneously cold, dense, and slow molecules for, e.g., high-resolution spectroscopy and controlled-collision studies. The talk presents most recent achievements obtained with the conceptually and technologically favorable class of symmetric-top molecules. Most important, with trapped CH₃F molecules in predominantly a single rotational and vibrational state, we reach the cold collision regime, understand the nature of the collision process, and control the collisions with an external field. Our achievement opens up new possibilities for a plethora of experiments in various research fields ranging from cold chemistry to quantum information.   

Molecular rotational state spaces for quantum information processing

Rotational states of symmetric and asymmetric molecules, modeled by infinite-dimensional Hilbert spaces of various quantum rotors, present new grounds for encoding and processing quantum information. Development of a physical and mathematical framework adapted for quantum applications in rotational systems is currently in its infancy. I discuss how to adapt basic quantum tools from discrete- and continuous-variable systems to symmetric molecules, developing a set of “position-state” labels for molecular orientations and a Pauli-type group of unitary operations. With an eye on quantum error correction, I discuss ongoing efforts studying the nature of noise introduced by a thermal environment in these systems.