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Spectroscopy of ultracold LiRb molecules using ionization detection

Adeel Altaf

Published Jan 1, 2014• 2 citations
OpenAlex

Abstract

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.

Related papers

Formation of ultracold 7Li85Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy

Adeel Altaf, Sourav Dutta, John Lorenz +3 more

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.

arXiv:1409.2961•The Journal of Chemical Physics•Mar 19, 2015•20 citations

Experimental Studies of LiRb: Spectroscopy and Ultracold Molecule Formation by Photoassociation

Sourav Dutta

Heteronuclear polar molecules have recently attracted enormous attention owing to their ground state having a large electric dipole moment. The long range anisotropic dipole-dipole interaction in such systems is the basis for a variety of applications including quantum computing, precision measurements, ultracold chemistry and quantum simulations. Heteronuclear bi-alkali molecules, only a small subset of polar molecules, have received special attention mainly because the constituent alkali atoms are easy to laser cool and can be relatively easily associated to form molecules at ultracold temperatures. Our choice, the LiRb molecule, is motivated by the relatively high dipole moment (4.1 Debye) of the LiRb molecule in its rovibronic ground state. In this thesis, we study the LiRb molecule using laser spectroscopy and report, for the first time, the production of ultracold LiRb molecules by photoassociation (PA). The LiRb molecule is the least studied among all bi-alkali molecules and the first spectroscopic measurements on hot vapor phase LiRb molecules were reported only in 2011. We describe these measurements and their significance in chapter 2, after a brief introduction to the field of ultracold polar molecules in chapter 1. In chapter 3, we discuss our apparatus for simultaneous cooling and trapping of Li and Rb atoms in a dual-species magneto-optical trap (MOT) and report the measurement of interspecies collision-induced losses. In chapter 4, we describe the production of ultracold LiRb molecules in excited electronic states by photoassociation (PA). We report the measurements of the C6 coefficients for the Li (2s 2S1/2) + Rb (5p 2P1/2) and the Li (2s 2S1/2) + Rb (5p 2P3/2) asymptotes. We find a molecule formation rate (PLiRb) as high as 3.5x107 s-1 and a PA rate coefficient (KPA) as high as 1.3x10-10 cm3/s, the highest among heteronuclear bi-alkali molecules. In chapter 5, we discuss results on two-photon PA and we conclude, in chapter 6, with a road roadmap of future experiments for the production and detection of ultracold LiRb molecules in their rovibronic ground state.

•Jan 1, 2013•4 citations

Formation of deeply bound LiRb molecules via photoassociation to near asymptotic states

John Lorenz

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.

•Jan 1, 2014•1 citation

Production of ultracold heteronuclear KRb molecules

Dajun Wang

This thesis describes the spectroscopy work on ultracold 39K 85Rb molecules as part of our effort towards producing ground-state ultracold polar molecules. ^ The starting points of our experiment are laser cooled and trapped K and Rb atoms in dual-species MOTs and the molecule formation method is photoassociation (PA). A fraction of the PA-produced excited-state molecules can spontaneously emit to the two lowest electronic states, the X 1Σ + state and the a 3Σ + state, to form high vibrational level molecules. In order to develop a population transfer scheme to make deeply bound molecules, we have studied the spectroscopy of KRb in several steps. Besides the PA step, we have also carried out a state-selective detection experiment to study the population distribution of the high vibrational level molecules formed via spontaneous emission. The detection method is pulsed-laser based ion time-of-flight mass spectroscopy. Due to the linewidth limitations of the pulsed laser, this detection method can only resolve vibrational structures. A cw laser induced ion depletion spectroscopy technique has been developed in order to obtain rotational resolution. Using this ion depletion method, we have studied a possible stimulated Raman transfer scheme via the 3 1Σ+ state. To this end, we have obtained all the spectroscopic information required to produce deeply bound KRb molecules in a single vibrational and rotational level. ^ Several other spectroscopic studies using the high vibrational level ultracold molecules are also discussed. ^

•Jan 1, 2007•0 citations

Photoassociation of ultracold LiRb * molecules: Observation of high efficiency and unitarity-limited rate saturation

Sourav Dutta, John Lorenz, Adeel Altaf +2 more

We report the production of ultracold heteronuclear $^{7}\mathrm{Li}^{85}\mathrm{Rb}$ molecules in excited electronic states by photoassociation (PA) of ultracold $^{7}\mathrm{Li}$ and $^{85}\mathrm{Rb}$ atoms. PA is performed in a dual-species $^{7}\mathrm{Li}$-$^{85}\mathrm{Rb}$ magneto-optical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2$s$ ${}^{2}$${S}_{1/2}$) + Rb (5$p$ ${}^{2}{P}_{3/2}$) asymptote and experimentally determine the long range ${C}_{6}$ dispersion coefficients. We find a molecule formation rate (${P}_{\mathrm{LiRb}}$) of 3.5 \ifmmode\times\else\texttimes\fi{} 10${}^{7}$ s${}^{\ensuremath{-}1}$ and a PA rate coefficient (${K}_{\mathrm{PA}}$) of 1.3 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}10}$ cm${}^{3}$/s, the highest among heteronuclear bi-alkali-metal molecules. At large PA laser intensity we observe the saturation of the PA rate coefficient (${K}_{\mathrm{PA}}$) close to the theoretical value at the unitarity limit.

arXiv:1311.6297•Physical Review A•Feb 19, 2014•39 citations

Formation of deeply bound ultracold LiRb molecules via photoassociation near the Li 2 S 1 / 2 + Rb 5 P 3 / 2 asymptote

John Lorenz, Adeel Altaf, Sourav Dutta +2 more

We present spectra of ultracold $^{7}\mathrm{Li}^{85}\mathrm{Rb}$ molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual-species magneto-optical trap, weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the ${B}^{1}\ensuremath{\Pi}$ state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the observed lines from the spectra are consistent with transitions from the ${X}^{1}{\ensuremath{\Sigma}}^{+}$ ground electronic state to either the ${B}^{1}\ensuremath{\Pi}$ or the ${D}^{1}\ensuremath{\Pi}$ electronic state that has been previously observed, with levels possibly as low as ${X}^{1}{\ensuremath{\Sigma}}^{+}({v}^{\ensuremath{'}\ensuremath{'}}=2)$ being populated. We do not observe decay to weakly bound vibrational levels of the ${X}^{1}{\ensuremath{\Sigma}}^{+}$ or ${a}^{3}{\ensuremath{\Sigma}}^{+}$ electronic state in the spectra. We also deduce a lower bound of $3900 \mathrm{cm}{}^{\ensuremath{-}1}$ for the dissociation energy of the $\mathrm{LiRb}{}^{+}$ molecular ion.

arXiv:1410.4862•Physical Review A•Dec 19, 2014•12 citations
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.
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.
Heteronuclear polar molecules have recently attracted enormous attention owing to their ground state having a large electric dipole moment. The long range anisotropic dipole-dipole interaction in such systems is the basis for a variety of applications including quantum computing, precision measurements, ultracold chemistry and quantum simulations. Heteronuclear bi-alkali molecules, only a small subset of polar molecules, have received special attention mainly because the constituent alkali atoms are easy to laser cool and can be relatively easily associated to form molecules at ultracold temperatures. Our choice, the LiRb molecule, is motivated by the relatively high dipole moment (4.1 Debye) of the LiRb molecule in its rovibronic ground state. In this thesis, we study the LiRb molecule using laser spectroscopy and report, for the first time, the production of ultracold LiRb molecules by photoassociation (PA). The LiRb molecule is the least studied among all bi-alkali molecules and the first spectroscopic measurements on hot vapor phase LiRb molecules were reported only in 2011. We describe these measurements and their significance in chapter 2, after a brief introduction to the field of ultracold polar molecules in chapter 1. In chapter 3, we discuss our apparatus for simultaneous cooling and trapping of Li and Rb atoms in a dual-species magneto-optical trap (MOT) and report the measurement of interspecies collision-induced losses. In chapter 4, we describe the production of ultracold LiRb molecules in excited electronic states by photoassociation (PA). We report the measurements of the C6 coefficients for the Li (2s 2S1/2) + Rb (5p 2P1/2) and the Li (2s 2S1/2) + Rb (5p 2P3/2) asymptotes. We find a molecule formation rate (PLiRb) as high as 3.5x107 s-1 and a PA rate coefficient (KPA) as high as 1.3x10-10 cm3/s, the highest among heteronuclear bi-alkali molecules. In chapter 5, we discuss results on two-photon PA and we conclude, in chapter 6, with a road roadmap of future experiments for the production and detection of ultracold LiRb molecules in their rovibronic 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.
This thesis describes the spectroscopy work on ultracold 39K 85Rb molecules as part of our effort towards producing ground-state ultracold polar molecules. ^ The starting points of our experiment are laser cooled and trapped K and Rb atoms in dual-species MOTs and the molecule formation method is photoassociation (PA). A fraction of the PA-produced excited-state molecules can spontaneously emit to the two lowest electronic states, the X 1Σ + state and the a 3Σ + state, to form high vibrational level molecules. In order to develop a population transfer scheme to make deeply bound molecules, we have studied the spectroscopy of KRb in several steps. Besides the PA step, we have also carried out a state-selective detection experiment to study the population distribution of the high vibrational level molecules formed via spontaneous emission. The detection method is pulsed-laser based ion time-of-flight mass spectroscopy. Due to the linewidth limitations of the pulsed laser, this detection method can only resolve vibrational structures. A cw laser induced ion depletion spectroscopy technique has been developed in order to obtain rotational resolution. Using this ion depletion method, we have studied a possible stimulated Raman transfer scheme via the 3 1Σ+ state. To this end, we have obtained all the spectroscopic information required to produce deeply bound KRb molecules in a single vibrational and rotational level. ^ Several other spectroscopic studies using the high vibrational level ultracold molecules are also discussed. ^
We report the production of ultracold heteronuclear 7Li85Rb^{7}\mathrm{Li}^{85}\mathrm{Rb}7Li85Rb molecules in excited electronic states by photoassociation (PA) of ultracold 7Li^{7}\mathrm{Li}7Li and 85Rb^{85}\mathrm{Rb}85Rb atoms. PA is performed in a dual-species 7Li^{7}\mathrm{Li}7Li-85Rb^{85}\mathrm{Rb}85Rb magneto-optical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2sss 2{}^{2}2S1/2{S}_{1/2}S1/2​) + Rb (5ppp 2P3/2{}^{2}{P}_{3/2}2P3/2​) asymptote and experimentally determine the long range C6{C}_{6}C6​ dispersion coefficients. We find a molecule formation rate (PLiRb{P}_{\mathrm{LiRb}}PLiRb​) of 3.5 \ifmmode\times\else\texttimes\fi{} 107{}^{7}7 s${}^{\ensuremath{-}1}$ and a PA rate coefficient (KPA{K}_{\mathrm{PA}}KPA​) of 1.3 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}10}$ cm3{}^{3}3/s, the highest among heteronuclear bi-alkali-metal molecules. At large PA laser intensity we observe the saturation of the PA rate coefficient (KPA{K}_{\mathrm{PA}}KPA​) close to the theoretical value at the unitarity limit.
We present spectra of ultracold 7Li85Rb^{7}\mathrm{Li}^{85}\mathrm{Rb}7Li85Rb molecules in their electronic ground state formed by spontaneous decay of weakly bound photoassociated molecules. Beginning with atoms in a dual-species magneto-optical trap, weakly bound molecules are formed in the 4(1) electronic state, which corresponds to the ${B}^{1}\ensuremath{\Pi}$ state at short range. These molecules spontaneously decay to the electronic ground state and we use resonantly enhanced multiphoton ionization to determine the vibrational population distribution in the electronic ground states after spontaneous emission. Many of the observed lines from the spectra are consistent with transitions from the ${X}^{1}{\ensuremath{\Sigma}}^{+}$ ground electronic state to either the ${B}^{1}\ensuremath{\Pi}$ or the ${D}^{1}\ensuremath{\Pi}$ electronic state that has been previously observed, with levels possibly as low as ${X}^{1}{\ensuremath{\Sigma}}^{+}({v}^{\ensuremath{'}\ensuremath{'}}=2)$ being populated. We do not observe decay to weakly bound vibrational levels of the ${X}^{1}{\ensuremath{\Sigma}}^{+}$ or ${a}^{3}{\ensuremath{\Sigma}}^{+}$ electronic state in the spectra. We also deduce a lower bound of $3900 \mathrm{cm}{}^{\ensuremath{-}1}$ for the dissociation energy of the LiRb+\mathrm{LiRb}{}^{+}LiRb+ molecular ion.