We study the rovibronic transitions in NaK 2 between its electronic ground state 1 2 A ′ and its second excited state 3 2 A ′ , to identify possible pathways for the creation of ultracold ground-state triatomic molecules. Our methodology relies on the computation of potential energy surfaces and transition dipole moment surfaces for the relevant electronic states using methods. Rovibrational energy levels and wave functions are determined using the discrete variable representation approach. A double-well structure of the potential energy surface is identified for both states, and the related transition strengths between the rovibrational levels are derived. Our calculations show that the formation of ultracold ground-state NaK 2 molecules is expected when starting from an excited electronic state of NaK 2 , which can be created by photoassociation of NaK and K, as observed by optical means by Cao, [].
We study the rovibronic transitions in NaK 2 between its electronic ground state 1 2 A ′ and its second excited state 3 2 A ′ , to identify possible pathways for the creation of ultracold ground-state triatomic molecules. Our methodology relies on the computation of potential energy surfaces and transition dipole moment surfaces for the relevant electronic states using methods. Rovibrational energy levels and wave functions are determined using the discrete variable representation approach. A double-well structure of the potential energy surface is identified for both states, and the related transition strengths between the rovibrational levels are derived. Our calculations show that the formation of ultracold ground-state NaK 2 molecules is expected when starting from an excited electronic state of NaK 2 , which can be created by photoassociation of NaK and K, as observed by optical means by Cao, [].
We explore possible pathways for the creation of ultracold polar NaK molecules in their absolute electronic and rovibrational ground state starting from ultracold Feshbach molecules. In particular, we present a multichannel analysis of the electronic ground and K(4p)+Na(3s) excited-state manifold of NaK, analyze the spin character of both the Feshbach molecular state and the electronically excited intermediate states and discuss possible coherent two-photon transfer paths from Feshbach molecules to rovibronic ground-state molecules. The theoretical study is complemented by the demonstration of stimulated Raman adiabatic passage from the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}^{+}$(v=0) state to the $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Sigma}}^{+}$ manifold on a molecular beam experiment.
The assembly and coherent control of ultracold molecules have opened new horizons in quantum science with applications in ultracold chemistry, quantum information, quantum simulation, precision metrology and fundamental physics. While considerable progress has been achieved in controlling diatomic molecules at ultracold temperatures, extending to atom-diatom collisions and triatomic systems introduces additional internal structure, anisotropy, and interaction complexity, enabling access to many-body phenomena. This dissertation presents a detailed theoretical study on the production and stabilization of ultracold alkali-metal triatomic molecules, with a particular focus on the NaK2 molecular species. First, long-range photoassociation in ultracold NaK(X^1Σ+) + K(4s) mixtures is investigated near the molecular transition X^1Σ+ → b^3Π. Photoassociation rates into weakly bound trimers in the electronically excited 3^2A' state are evaluated under experimentally relevant conditions. The calculated photoassociation rates indicate experimentally feasible and spectrally selective routes for detecting ultracold atom–diatom photoassociation resonances, while suppressing competing diatomic loss channels. Second, a microwave-assisted association mechanism is introduced for coherently binding ultracold atoms and polar molecules into weakly bound triatomic molecules on the ground-state 1^2A' potential energy surface. This process relies on the interaction between the electric component of the microwave field and the permanent electric dipole moment of the NaK molecule. In the presence of the anisotropic atom–diatom potential, which couples the molecular rotation to the relative angular motion, the microwave field can drive transitions from scattering states to weakly bound trimer states entirely in the electronic ground-state of the triatomic molecule, without involving spontaneous emission. This process is therefore intrinsically coherent and particularly suited to closed-shell polar molecules for which magnetically tunable Feshbach resonances are weak or absent. Finally, candidate pathways toward coherent population transfer to the absolute rovibronic ground state of NaK2 are explored using bridge states belonging to the excited 3^2A' electronic state, such as those identified in [Ref.1]. The relevant potential energy surfaces, transition dipole moments, and rovibrational structures are analyzed, revealing favorable conditions for future stimulated Raman adiabatic passage scheme. The theoretical modeling combines high-level electronic-structure calculations with nuclear-motion methods across multiple energy and length scales. Three-dimensional potential energy surfaces and electronic transition dipole moment surfaces were obtained from ab initio multireference configuration interaction calculations employing effective-core pseudopotentials and core-polarization potentials. Nuclear motion was treated using coupled-channel methods for describing weakly bound states and discrete variable representation methods for deeply bound rovibrational states. The resulting wavefunctions were subsequently used to evaluate Franck–Condon factors, photo- and microwave association rates, and transition strengths relevant to experimental implementation. Overall, this dissertation provides an extensive theoretical framework for the formation, detection and ground-state stabilization of ultracold NaK2 trimers. Reference: [1] J. Cao, B.-Y. Wang, H. Yang, Z.-J. Fan, Z. Su, J. Rui, B. Zhao, and J.-W. Pan, “Observation of photoassociation resonances in ultracold atom-molecule collisions,” Phys. Rev. Lett., vol. 132, p. 093403, 2024.
Abstract We spectroscopically investigate a pathway for the conversion of 23Na39K Feshbach molecules into rovibronic ground state molecules via stimulated Raman adiabatic passage. Using photoassociation spectroscopy from the diatomic scattering threshold in the a 3Σ+ potential, we locate the resonantly mixed electronically excited intermediate states ∣ B 1 Π , v = 8 〉 and ∣ c 3 Σ + , v = 30 〉 which, due to their singlet–triplet admixture, serve as an ideal bridge between predominantly a 3Σ+ Feshbach molecules and pure X 1Σ+ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet–triplet coupling of these states. Using Autler–Townes spectroscopy, we locate the rovibronic ground state of the 23Na39K molecule ( ∣ X 1 Σ + , v = 0 , N = 0 〉 ) and the second rotationally excited state N = 2 to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic 23Na39K ground state molecules.
The creation of ultracold molecules is currently limited to diatomic species. In this Letter, we present a theoretical description of the photoassociation of ultracold atoms and molecules to create ultracold excited triatomic molecules, thus being a novel example of a light-assisted ultracold chemical reaction. The calculation of the photoassociation rate of an ultracold Cs_{2} molecule in its rovibrational ground state with an ultracold Cs atom at frequencies close to its resonant excitation is reported, based on the solution of the quantum dynamics involving the atom-molecule long-range interactions and assuming a model potential for the short-range physics. The rate for the formation of excited Cs_{3} molecules is predicted to be comparable with currently observed atom-atom photoassociation rates. We formulate an experimental proposal to observe this process relying on the available techniques of optical lattices and standard photoassociation spectroscopy.
We present a simple model of ultracold cesium dimer formation in which the photoassociation into rovibrational levels of the double-minimum Cs2 $3{}^{1}{\ensuremath{\Sigma}}_{u}^{+}$ state above its internal barrier enables spontaneous or stimulated emission into the lowest rovibrational levels of the Cs2 $1(X){}^{1}{\ensuremath{\Sigma}}_{g}^{+}$ ground electronic state. The transition dipole moment should be sufficiently large for observation of such spectral transitions. The use of the Cs2 $3{}^{1}{\ensuremath{\Sigma}}_{u}^{+}$ double-minimum potential could be extended to molecular Bose-Einstein condensates in which an optical trap can be employed for trapping of both atomic and molecular species.
A model for photoassociation of ultracold atoms and molecules is presented, and applied to the case of 39K and 23Na39K bosonic particles. The model relies on the assumption that photoaossociation is dominated by long-range atom-molecule interactions, well outside the chemical bond region. The frequency of the photoassociation laser is chosen close to a bound-bound rovibronic transition from the X1Σ+ ground state toward the metastable b3Π lowest excited state of 23Na39K, allowing to neglect any other excitation which could hinder the photoassociation detection. The energy level structure of the long-range 39K⋯23Na39K excited super-dimer is computed in the space-fixed frame by solving coupled-channel equations, involving the coupling between the 23Na39K internal rotation with the mechanical rotation of the super-dimer complex. A quite rich structure is obtained, and the corresponding photoassociation rates are presented. Other possible photossociation transitions are discussed in the context of the proposed model.