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arXiv:1607.04608 · The Journal of Chemical Physics

The d 3Π state of LiRb

Ian Stevenson, David Blasing, Adeel Altaf, Yong P. Chen, Daniel S. Elliott

Published Dec 8, 2016• 5 citations
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Abstract

We report our spectroscopic studies of the d 3Π state of ultra-cold 7Li85Rb using resonantly enhanced multi-photon ionization and depletion spectroscopy with bound-to-bound transitions originating from the metastable a 3Σ+ state. We evaluate the potential of this state for use as the intermediate state in a stimulated-Raman-adiabatic-passage transfer scheme from triplet Feshbach LiRb molecules to the X 1Σ+ ground state and find that the lowest several vibrational levels possess the requisite overlap with initial and final states, as well as convenient energies. Using depletion measurements, we measured the well depth and spin-orbit splitting. We suggest possible pathways for short-range photoassociation using deeply bound vibrational levels of this electronic state.

DOI
10.1063/1.4964655

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We report our spectroscopic studies of the d 3Π state of ultra-cold 7Li85Rb using resonantly enhanced multi-photon ionization and depletion spectroscopy with bound-to-bound transitions originating from the metastable a 3Σ+ state. We evaluate the potential of this state for use as the intermediate state in a stimulated-Raman-adiabatic-passage transfer scheme from triplet Feshbach LiRb molecules to the X 1Σ+ ground state and find that the lowest several vibrational levels possess the requisite overlap with initial and final states, as well as convenient energies. Using depletion measurements, we measured the well depth and spin-orbit splitting. We suggest possible pathways for short-range photoassociation using deeply bound vibrational levels of this electronic state.
We report our spectroscopic studies of the d3Πd ^3\Pid3Π state of ultra-cold 7^77Li85^{85}85Rb using resonantly-enhanced multi-photon ionization and depletion spectroscopy with bound-to-bound transitions originating from the metastable a3Σ+a ^3\Sigma^+a3Σ+ state. We evaluate the potential of this state for use as the intermediate state in a STIRAP transfer scheme from triplet Feshbach LiRb molecules to the X1Σ+X ^1\Sigma^+X1Σ+ ground state, and find that the lowest several vibrational levels possess the requisite overlap with initial and final states, as well as convenient energies. Using depletion measurements, we measured the well depth and spin-orbit splitting. We suggest possible pathways for short-range photoassociation using deeply-bound vibrational levels of this electronic state.
We report the formation of ultracold (7)Li(85)Rb molecules in the a(3)Σ(+) electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ∼62 cm(-1) below the (7)Li 2s (2)S1/2 + (85)Rb 5p (2)P1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a(3)Σ(+) state and excited electronic 3(3)Π and 4(3)Σ(+) states and identify a(3)Σ(+) (v″ = 7-13), 3(3)Π (vΠ' = 0-10), and 4(3)Σ(+) (vΣ' = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.
We present the results of a spectroscopic study LiRb molecules created via photoassociation (PA) to vibration levels of the 4(1) potential. Atoms are first cooled and trapped in a dual species 7Li/ 85Rb magneto-optical trap (MOT) at temperatures of ≈ 1 mK or less. In a cold sample of sufficient density, PA occurs when a resonant laser field induces a free-bound transition to create molecules in an excited electronic potential. After spontaneous emission the molecules decay to a mixture of free atoms and bound molecules depending on the Franck-Condon factors (FCFs) of the excited and ground state vibrational wavefunctions. While excited LiRb * has been previously detected by trap loss fluorescence detection, ionization spectroscopy is required to determine the population of ground state levels after decay. We detect ground state molecules via resonantly enhanced multiphoton ionization (REMPI) where a two photon ionization transition is enhanced by an intermediate resonance. The intermediate resonances match progressions from the D1Π and possibly B1&Pgr; potentials, many of which have known energies obtained from previous heat pipe experiments. This is contrary to the expectation that weakly bound LiRb * should primarily decay to weakly bound levels of the ground state and could point to a possible path for creating molecules in the rovibronic ground state.
We present spectroscopic studies of ultracold LiRb molecules using ionization detection. The molecules are created by cooling and trapping Li and Rb atoms in overlapping magneto-optical traps (MOTs) and using light resonant with a free-bound transition to create weakly bound excited state molecules in a process known as photoassociation (PA). We explore weakly bound vibrational levels of LiRb with PA spectroscopy using ionization detection and, where possible, compare our results with earlier measurements performed in our lab using trap-loss spectroscopy. In addition, we also probe vibrational levels of the ground triplet electronic state and excited electronic states using resonantly enhanced multiphoton ionization (REMPI) spectroscopy. We identify several vibrational levels of the α3Σ+, (3)3ΠΩ and (4)3Σ + states and compare our observations with theoretical calculations. As LiRb is one of the least studied heteronuclear diatomic molecules, these studies are aimed towards exploring the molecular structure. The spectroscopic work is also in line with the long-term project goals of transferring ultracold LiRb molecules into the lowest rotational and vibrational levels of the ground singlet electronic state. Molecules in this rovibronic ground state possess a large electric dipole moment, which is essential for application of ultracold molecules in various quantum computation schemes. The rovibronic ground state will also be an ideal starting point for investigating molecular entangled states.
I present spectroscopic data on ultracold lithium-rubidium molecules in a dual species magneto-optical-trap in order to find suitable intermediate states to transfer population to the rotational, vibrational and electronic ground state via a stimulated Raman process. First, I improved the accuracy of the energetic location of the ground state by two orders of magnitude using photoassociation as a spectroscopic tool to measure the energy of bound states relative to the scattering continuum. Second, we studied the d 3Π-D 1Π and A 1Σ+ -b 3Π0+ excited electronic manifolds with a combination of resonantly-enhancedmulti-photon-ionization and depletion spectroscopy finding suitable singlet-triplet mixed states to use in the Raman transfer scheme. Finally, I demonstrate robust optical phase locked loops to maintain the coherence between the two lasers required for the Raman process.
This thesis describes a suite of experimental tools and spectroscopic measurements performed on ultracold ⁶Li molecules. The aim is to create the necessary ingredients for the coherent transfer of the population of ultracold, weakly bound, Feshbach molecules of ⁶Li to deeply bound ro-vibrational levels, making the eventual creation of a Bose-Einstein condensate (BEC) of ground state lithium dimers a reality at the University of British Columbia. Some of the technological milestones include the development of a unique laser system consisting of two Ti:Sapphire lasers frequency stabilized to a femtosecond frequency comb as well as the demonstration of the first in Canada BEC of Feshbach molecules. To determine a suitable path for the coherent transfer using stimulated Raman adiabatic passage (STIRAP) we measure the binding energies of the vibrational levels v''=20-26 of the c(1³Ʃ+g) and v''=29-35 of the A(1¹Ʃ+u) excited states of lithium dimers by the photoassociation of a degenerate Fermi gas of 6Li atoms, achieving accuracy of 600 kHz. For each vibrational level of the triplet potential, we resolve the rotational structure using a Feshbach resonance to enhance the photoassociation rates from p-wave collisions. We also, for the first time, determine the spin-spin and spin-rotation interaction constants for this state. Finally, we are the first to demonstrate exotic dark states in quantum gases of fermionic lithium where atom-molecule coherence is produced between a deeply bound singlet (or triplet) molecular level and atomic pairs in a weakly interacting Fermi gas at zero gauss or in the BEC-BCS crossover regime (i.e. Feshbach molecules or BCS-like pairs). We observe an abrupt and unanticipated change of the classic EIT signature (Electromagnetically Induced Transparency) of the dark-state (i.e. the suppression of single photon absorption to the excited state) in the vicinity of the broad Feshbach resonance at 832.2 gauss potentially indicating new physics not previously considered.