Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L26: Nonadiabatic Dynamics in Cold and Ultracold Collisions and Reactions IFocus Live
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Sponsoring Units: DCP Chair: Hua Guo, University of New Mexico |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L26.00001: Collisions of ultracold RbCs molecules Phil Gregory, Jacob Blackmore, Sarah Louise Bromley, Matthew Frye, Jeremy Hutson, Simon Cornish Ultracold polar molecules offer many exciting opportunities in the fields of quantum computation, quantum simulation and fundamental studies of quantum matter. Long-lived, trapped samples of molecules are crucial to many of these applications. Yet, remarkably, the nature of the collisions between molecules is poorly understood, with fast loss being observed even for chemically stable molecules such as RbCs. Here we report measurements of collisional loss in gases of ultracold RbCs molecules confined in an optical trap. We study both molecule-molecule collisions and atom-molecule collisions. For molecule-molecule collisions we present evidence that pairs of molecules form long-lived collision complexes that are lost due to fast optical excitation by the dipole trapping light. with both Rb and Cs. For atom-molecule collisions we investigate both reactive Rb+RbCs and nonreactive Cs+RbCs collisions, comparing our results to simple single-channel models with short-range loss. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L26.00002: Which form of the molecular Hamiltonian is the most suitable for simulating the nonadiabatic quantum dynamics at a conical intersection? Seonghoon Choi, Jiri Vanicek Choosing a suitable representation of the molecular Hamiltonian is a challenge faced by simulations of the nonadiabatic quantum dynamics around a conical intersection. The adiabatic, exact quasidiabatic, and strictly diabatic representations are exact, whereas the approximate quasidiabatic Hamiltonian ignores the residual nonadiabatic couplings. A rigorous numerical comparison of these four representations is difficult due to the exceptional nature of systems where these can be defined exactly and the necessity of an accurate algorithm that avoids mixing numerical errors with errors due to the different representations. We are able to perform this comparison [1] using the quadratic Jahn-Teller model and high-order geometric integrators [2,3] and find that only the rarely employed exact quasidiabatic Hamiltonian yields nearly identical results as the strictly diabatic Hamiltonian, which is unavailable in general. In this model and with the same grid, the approximate quasidiabatic Hamiltonian led to inaccurate wavepacket dynamics, while the adiabatic Hamiltonian was the least accurate due to the singular nonadiabatic couplings. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L26.00003: Mechanistic Insights into Geometric Phase Effects in the Ultracold O + OH Reaction Jiayu Huang, Brian Kendrick, Dong H. Zhang The quantum-enhanced geometric phase (GP) effects in ultracold reaction systems have attracted much recent attention owing to its potential application in controlling ultracold chemistry. We performed the time-dependent wave packet (TDWP) dynamical calculations for the ultracold O + OH reaction with the inclusion of the GP. The calculation illustrates that the TDWP method accurately describes experimentally relevent ultracold reaction systems containing a conical intersection (CI). More interestingly, the scattering wave functions provided by the TDWP method reveal explicitly the nature of the quantum interference between the direct and looping reaction pathways around the CI, and thus confirms the dynamical origin of the GP effects in the reaction for the first time. We will discuss how the ultracold O + OH reaction proceeds under the control of the GP. These findings indicate that quantum control techniques such as an optical lattice trap or the initial state orientation should be effective in controlling the reactivity. |
Wednesday, March 17, 2021 8:36AM - 9:12AM Live |
L26.00004: Sub-Kelvin Stereodynamics in merged neutral beams Invited Speaker: Andreas Osterwalder I will present our recent results on the sub-Kelvin stereodynamis of Penning ionisation and related reactions. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L26.00005: Resonant dipolar collisions of 23Na87Rb rotational mixtures Junyu He, Xin Ye, Jun Yu Lin, Mingyang Guo, Goulven Quéméner, Dajun Wang The resonant dipole-dipole interaction between polar molecules occupying rotational states of opposite parities is a valuable resource for quantum simulation and quantum information processing. In this talk, we report the investigation on the strong resonant dipolar collisions of ultracold bosonic 23Na87Rb molecules, in the absence of external electric field. The dramatically enhanced two-body loss rate constants we measured are in good agreement with quantum close-coupling calculations. In addition, the dipolar strength can be tuned by preparing the NaRb mixture in different rotational levels. When the rotational level combination is not of the lowest energy, contributions from hyperfine changing collisions are also observed. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L26.00006: Quantum state selectivity and magnetic tuning of the chemical reaction NaLi(a3 Σ+) + Na → Na2 + Li at ultralow temperatures Rebekah Hermsmeier, Jacek Klos, Svetlana Kotochigova, Timur Tscherbul Recent advances in controlling chemical reactivity of ultracold molecules [1,2] have motivated our study of spin-dependent chemical reactions in the presence of external magnetic fields. We present coupled-channel statistical calculations on the ultracold chemical reaction NaLi(a3 Σ+) + Na → Na2 + Li including the Zeeman and hyperfine structure of the reactants. The calculations are based on a set of NaLi-Na potential energy surfaces of quartet and doublet symmetries constructed from the accurate pairwise Na-Li and Na-Na interactions determined from ab initio calculations. We find that the reaction rates are highly sensitive to the initial hyperfine states of the reactants, and can be efficiently controlled by an external magnetic field. |
Wednesday, March 17, 2021 9:36AM - 10:12AM Live |
L26.00007: Non-adiabatic quantum dynamics of cold and ultracold chemical reactions Invited Speaker: Brian Kendrick Electronically non-adiabatic processes are usually associated with high energy molecular collisions and photodissociation. In contrast, for many of the cold/ultracold molecular systems of current experimental interest, an excited electronic state is energetically accessible even for collision temperatures approaching absolute zero. For these systems, a non-adiabatic fully quantum mechanical treatment is required that includes the two coupled electronic states. A recently developed non-adiabatic quantum dynamics methodology is discussed which is ideally suited for treating these systems. The methodology is applied to several ultracold chemical reactions under active experimental investigation, such as Li + LiNa → Li2 + Na. A novel quantum interference mechanism which is unique to ultracold collisions is shown to effectively control the reaction outcome due to the nearly maximal constructive or destructive interference (a quantum molecular switch!). Non-adiabatic effects are shown to reverse the nature of the interference leading to the opposite (correct) theoretical prediction of the ultracold rate coefficients. The highly non-linear nature and sensitivity of the quantum interference might be exploited by experimentalists via the application of external fields and/or the selection of a particular initial quantum state. Possible technological applications include quantum control, probing molecular interactions, sensing, and precision measurements. |
Wednesday, March 17, 2021 10:12AM - 10:48AM Live |
L26.00008: Precision Test of Statistical Phase Space theory in ultracold KRb bimolecular reactions Invited Speaker: Kang-Kuen Ni Advances in quantum manipulation of molecules bring unique opportunities, including the use of molecules to search for new physics, harnessing molecular resources for quantum engineering, and exploring chemical reactions in the ultra-low temperature regime. In this talk, I focus on the latter topic where we work toward a detailed microscopic picture of molecules transforming from one species to another. In particular, we developed pair-correlated reaction products detection. We map the complete state-to-state ultracold KRb+KRb -> K2+Rb2 reaction and compare it to statistical phase space theory. |
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