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Chinese Physics B

Theoretical analysis of the coupling between Feshbach states and hyperfine excited states in the creation of 23Na40K molecule*

Ya-Xiong Liu, Bo Zhao

Published Dec 18, 2019• 9 citations
Publisher

Abstract

We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of 23Na40K ground-state molecules. We use coupled-channel method to calculate the wave function of the Feshbach molecules, and give the short-range wave function of triplet component. The energies of the hyperfine excited states and the coupling strength between the Feshbach states and the hyperfine excited states are calculated. Our results can be used to prepare a specific hyperfine level of the rovibrational ground state to study the ultracold collisions involving molecules.

DOI
10.1088/1674-1056/ab6314

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We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of 23Na40K ground-state molecules. We use coupled-channel method to calculate the wave function of the Feshbach molecules, and give the short-range wave function of triplet component. The energies of the hyperfine excited states and the coupling strength between the Feshbach states and the hyperfine excited states are calculated. Our results can be used to prepare a specific hyperfine level of the rovibrational ground state to study the ultracold collisions involving molecules.
We report a detailed molecular spectroscopy study of the lowest excited electronic states of 23Na87Rb^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{87}\mathrm{Rb}23Na87Rb for producing ultracold 23Na87Rb^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{87}\mathrm{Rb}23Na87Rb molecules in the electronic, rovibrational, and hyperfine ground state. Starting from weakly bound Feshbach molecules, a series of vibrational levels of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}\text{\ensuremath{-}}b{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ coupled excited states is investigated. After resolving, modeling, and interpreting the hyperfine structure of several lines, we successfully identify a long-lived level resulting from the accidental hyperfine coupling between the 0+{0}^{+}0+ and ${0}^{\ensuremath{-}}$ components of the $b{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ state, satisfying all the requirements for the population transfer toward the lowest rovibrational level of the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state. Using two-photon spectroscopy, its binding energy is measured to be 4977.308(3) ${\mathrm{cm}}^{\ensuremath{-}1}$. We calibrate all the transition strengths carefully and also demonstrate Raman transfer of Feshbach molecules to the absolute ground state.
K) molecules in the rovibrational ground state. We prepare the atoms and molecules in various hyperfine levels of their ground states and observe the loss of molecules as a function of the magnetic field. The atom-molecule Feshbach resonances are identified by observing an enhancement of the loss. We have observed 11 resonances in the magnetic field range of 43 to 120 gauss. The observed atom-molecule Feshbach resonances at ultralow temperatures probe the three-body potential energy surface with exceptional resolution and will help to improve understanding of ultracold collisions.
We report on high-resolution spectroscopy of ultracold fermionic 23 Na 40 K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B 1 Π ∼ c 3 Σ + intermediate state.Photoassociation in a 23 Na-40 K atomic mixture and one-photon spectroscopy on 23 Na 40 K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c 3 Σ + state.Two of these levels are found to be strongly perturbed by nearby B 1 Π levels via spinorbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex. The dominantly singlet level is used to locate the absolute rovibrational singlet ground state v J X 0, 0via Autler-Townes spectroscopy.We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state.Its binding energy is measured to be 5212.0447(1)cm -1 , a thousand-fold improvement in accuracy compared to previous determinations.In their absolute singlet ground state, 23 Na 40 K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye.Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.
We report on the creation of an ultracold dipolar gas of fermionic 23Na40 K molecules in their absolute rovibrational and hyperfine ground state. Starting from weakly bound Feshbach molecules, we demonstrate hyperfine resolved two-photon transfer into the singlet X 1Σ+|v=0,J=0⟩ ground state, coherently bridging a binding energy difference of 0.65 eV via stimulated rapid adiabatic passage. The spin-polarized, nearly quantum degenerate molecular gas displays a lifetime longer than 2.5 s, highlighting NaK's stability against two-body chemical reactions. A homogeneous electric field is applied to induce a dipole moment of up to 0.8 D. With these advances, the exploration of many-body physics with strongly dipolar Fermi gases of 23Na40K molecules is within experimental reach.
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.
Collisional resonances of molecules can offer a deeper understanding of interaction potentials and collision complexes, and allow control of chemical reactions.Here, we experimentally map out the spectrum of Feshbach resonances in collisions between ultracold triplet rovibrational ground-state NaLi molecules and Na atoms over a range of 1400 G. Preparation of the spin-stretched state puts the system initially into the nonreactive quartet potential.A total of 25 resonances are observed, in qualitative agreement with quantum-chemistry calculations using a coupled-channels approach.Although the theory cannot predict the positions of resonances, it can account for several experimental findings and provide unprecedented insight into the nature and couplings of ultracold, strongly interacting complexes.Previous work has addressed only weakly bound complexes.We show that the main coupling mechanism results from spin-rotation and spin-spin couplings in combination with the anisotropic atom-molecule interaction, and that the collisional complexes which support the resonances have a size of 30a 0 -40a 0 .This study illustrates the potential of a combined experimental and theoretical approach.