We demonstrate a two-photon pathway to the ground state of 6 Li 40 K molecules that involves only singlet-to-singlet optical transitions.We start from a molecular state which contains a significant admixture from the singlet ground state potential by selecting the Feshbach resonance for molecule association.With the only contributing singlet state to the molecular state being fully stretched and with control over the lasers polarization we address a sole hyperfine component of the excited A 1 Σ + potential without resolving its hyperfine structure.This scheme ensures access to only one ground state hyperfine component with sufficient Franck-Condon factors and moderate laser powers for both coupling transitions.Its implementation results in large and balanced Rabi frequencies, a favourable condition for the coherent transfer to the ground state.We perform dark resonance spectroscopy to precisely determine the transition frequencies of the states involved.The strong dipolar nature of 6 Li 40 K is revealed by Stark spectroscopy, as it is necessary for the study of dipolar interactions in an optical lattice.
We demonstrate a two-photon pathway to the ground state of 6 Li 40 K molecules that involves only singlet-to-singlet optical transitions.We start from a molecular state which contains a significant admixture from the singlet ground state potential by selecting the Feshbach resonance for molecule association.With the only contributing singlet state to the molecular state being fully stretched and with control over the lasers polarization we address a sole hyperfine component of the excited A 1 Σ + potential without resolving its hyperfine structure.This scheme ensures access to only one ground state hyperfine component with sufficient Franck-Condon factors and moderate laser powers for both coupling transitions.Its implementation results in large and balanced Rabi frequencies, a favourable condition for the coherent transfer to the ground state.We perform dark resonance spectroscopy to precisely determine the transition frequencies of the states involved.The strong dipolar nature of 6 Li 40 K is revealed by Stark spectroscopy, as it is necessary for the study of dipolar interactions in an optical lattice.
Starting from weakly bound Feshbach molecules, we demonstrate a two-photon pathway to the dipolar ground state of bi-alkali molecules that involves only singlet-to-singlet optical transitions. This pathway eliminates the search for a suitable intermediate state with sufficient singlet-triplet mixing and the exploration of its hyperfine structure, as is typical for pathways starting from triplet dominated Feshbach molecules. By selecting a Feshbach state with a stretched singlet hyperfine component and controlling the laser polarizations, we assure coupling to only single hyperfine components of the A^{1}Σ^{+} excited potential and the X^{1}Σ^{+} rovibrational ground state. In this way an ideal three level system is established, even if the hyperfine structure is not resolved. We demonstrate this pathway with ^{6}Li^{40}K molecules, and discuss its application to other important molecular species.
We report the creation of ultracold ground state ^{6}Li^{40}K polar molecules with high efficiency. Starting from weakly bound molecules, stimulated Raman adiabatic passage is adopted to coherently transfer the molecules to their singlet rovibrational ground state |X^{1}Σ^{+},v=0,J=0⟩. By employing a singlet stimulated Raman adiabatic passage pathway and low-phase-noise narrow-linewidth lasers, we observed a one-way transfer efficiency of 96(4)%. Held in an optical dipole trap, the lifetime of the ground state molecules is measured to be 5.0(3) ms. The large permanent dipole moment of LiK is confirmed by applying a dc electric field on the molecules and performing Stark shift spectroscopy of the ground state. With recent advances in the quantum control of collisions, our work paves the way for exploring quantum many-body physics with strongly interacting ^{6}Li^{40}K molecules.
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.
The production of a quantum gas with strong long - range dipolar interactions is a major scientific goal in the research field of ultracold gases. In their ro - vibrational ground state Li -K dimers possess a large permanent dipole moment, which could possibly be exploited for the realization of such a quantum gas. A production of these molecules can be achieved by the association of Li and K at a Feshbach resonance, followed by a coherent state transfer. In this thesis, detailed theoretical an experimental preparations to achieve state transfer by means of Stimulated Raman Adiabatic Passage (STIRAP) are described. The theoretical preparations focus on the selection of an electronically excited molecular state that is suitable for STIRAP transfer. In this context, molecular transition dipole moments for both transitions involved in STIRAP transfer are predicted for the first time. This is achieved by the calculation of Franck -Condon factors and a determination of the state in which the 6Li - 40K Feshbach molecules are produced. The calculations show that state transfer by use of a single STIRAP sequence is experimentally very well feasible. Further, the optical wavelengths that are needed to address the selected states are calculated. The high accuracy of the data will allow to carry out the molecular spectroscopy in a fast and efficient manner. Further, only a comparatively narrow wavelength tuneability of the spectroscopy lasers is needed. The most suitable Feshbach resonance for the production of 6Li - 40K molecules at experimentally manageable magnetic field strengths is occurring at 155G. Experimentally, this resonance is investigated by means of cross - dimensional relaxation. The application of the technique at various magnetic field strengths in the vicinity of the 155G Feshbach resonance allows a determination of the resonance position and width with so far unreached precision. This reveals the production of molecules on the atomic side of the resonance, thereby establishing the first observation of a many body effect in the crossover regime of a narrow Feshbach resonance. Further, mass dependent factors, with which the equilibration of an induced anisotropic temperature of the trapped particle samples can be described, are experimentally determined for the first time. The type of resonance as well as the measured molecular lifetimes are found to be very well suited for STIRAP transfer. A Raman laser system is designed based on the transition wavelengths and durations of state transfer which are predicted. As the wavelengths of the Raman lasers differ widely but coherence of the light fields is needed, the technical realization of a laser system is challenging. As a part of the laser system, the construction and characterization of a reference optical resonator are presented. Laser frequency stabilization with a linewidth of approximately 500Hz and an Allan deviation below 10−12 for timespans up to several ten seconds are demonstrated. Further, the stabilization of a frequency comb to this reference laser is demonstrated. For the laser spectroscopy of electronically excited Li -K states an interferometric laser frequency stabilization will be used. The device is a commercial design, for which a calibration procedure that enhances the precision by several orders of magnitude is worked out within this thesis. The calibration scheme includes the precise measurement of the stabilization’s wavelength dependent frequency deviations by means of a frequency comb. By the implementation of several calibration steps a remaining frequency deviation of less than 5.7MHz (rms 1.6MHz) in the whole relevant wavelength range 750 - 795 nm is achieved. Only the exceptional precision of the fully calibrated device permits the usage for the Li -K spectroscopy, while the demonstrated wide tuning capability facilitates the completion of the latter in a fast and convenient manner.
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.
Efficient Creation of Ultracold Ground State 6Li40K Polar Molecules
We report the creation of ultracold ground state 6Li40K polar molecules with high efficiency. Starting from weakly-bound molecules state, stimulated Raman adiabatic passage (STIRAP) is adopted to coherently transfer the molecules to their singlet ro-vibrational ground state ∣X1Σ+,v=0,J=0>. By employing a singlet STIRAP pathway and low-phase-noise narrow-linewidth lasers, we observed a one-way transfer efficiency of 96(4)\,\%. Held in an optical dipole trap, the lifetime of the ground-state molecules is measured to be 5.0(3)\,ms. The large permanent dipole moment of LiK is confirmed by applying a DC electric field on the molecules and performing Stark shift spectroscopy of the ground state. With recent advances in the quantum control of collisions, our work paves the way for exploring quantum many-body physics with strongly-interacting 6Li40K molecules.