Coherent Control of Ultracold Molecular Collisions: The Role of Resonances

Abstract

We consider the coherent control of ultracold molecule−molecule scattering, impacted by a dense set of rovibrational resonances. To characterize the resonance spectrum, a rudimentary model based on multichannel quantum defect theory has been used to study the control of the scattering cross section and the reaction rate. Complete control around resonance energies is shown to be possible, but thermal averaging over a large number of resonances significantly reduces the extent of control of reaction rates related to the random distribution of optimal control parameters between resonances. We show that measuring the extent of coherent control could be used to extract meaningful information about the relative contribution of direct scattering versus collision complex formation, as well as about the statistical regime.

Quantum stereodynamics of cold molecular collisions

“…Indeed, such interference effects have been theoretically demonstrated by Devolder, Tscherbul and Brumer for reactive scattering in F + H 2 /HD collisions and spin-relaxation in O 2 + O 2 collisions. 124,125 Control of reactive collisions in KRb + KRb collisions using a rudimentary model has also been explored by Devolder et al 126 In these theoretical studies reactant molecules are prepared in a coherent superposition of m j or spin states. We believe, this would be a next frontier in cold collisions where quantum effects are significantly amplified through coherent control and stereodynamic preparations.…”

A Hybrid Quantum-Classical Algorithm for Multichannel Quantum Scattering of Atoms and Molecules

“…38−41 and chemical reactions in ultracold environments may lead to novel ways to control them using, e.g., external electromagnetic fields 38−41 and/or quantum interference effects. 42,43 To model quantum scattering phenomena, one can use either time-independent or time-dependent (wavepacket) approaches. 24,26,44 Numerically exact quantum scattering simulations, in which the time-independent Schrodinger equation is solved directly via, e.g., coupled-channel methods or basis set expansion techniques, 24−26 are the "gold standard" of chemical physics, similar to the full configuration interaction or high-order coupled-cluster methods in quantum chemistry.…”

“…Quantum scattering phenomena play a fundamental role in physical and theoretical chemistry, being at the heart of gas-phase chemical reaction mechanisms, − astrochemistry, , combustion simulations, , mode-selective chemistry, , and atmospheric chemistry . In addition, molecular scattering experiments, particularly those performed at low and ultralow temperatures, provide the most detailed information about intermolecular interactions. − Molecular collisions and chemical reactions at ultralow temperatures determine the stability of ultracold molecular gases, with “good” (elastic) collisions leading to desirable thermalization and “bad” (inelastic) collisions responsible for undesirable trap losses, which limits the stability of trapped molecules. − A detailed understanding of the quantum dynamics of binary collisions and chemical reactions in ultracold environments may lead to novel ways to control them using, e.g., external electromagnetic fields − and/or quantum interference effects. , …”

Complete Quantum Coherent Control of Ultracold Molecular Collisions

“…For a given superposition determined by the parameters (η and β), some partial wave contributions (ℓm ℓ , ℓ ′ m ′ ℓ ) may experience constructive interference while others may exhibit destructive interference, suppressing the interference term in Eq. ( 9) [37]. This partial wave scrambling issue becomes more significant as the collision energy increases, along with the number of (ℓm ℓ , ℓ ′ m ′ ℓ ) contributions, and can result in complete loss of control.…”