We report the production of ultracold heteronuclear 7 Li 85 Rb molecules in excited electronic states by photoassociation (PA) of ultracold 7 Li and 85 Rb atoms. PA is performed in a dual-species 7 Li-85 Rb magnetooptical trap (MOT) and the PA resonances are detected using trap loss spectroscopy. We identify several strong PA resonances below the Li (2s 2 S 1/2 ) + Rb (5p 2 P 3/2 ) asymptote and experimentally determine the long range C 6 dispersion coefficients. We find a molecule formation rate (P LiRb ) of 3.5×10 7 s -1 and a PA rate coefficient (K PA ) of 1.3×10 -10 cm 3 /s, the highest among heteronuclear bi-alkali molecules. At large PA laser intensity, we observe the saturation of the PA rate coefficient (K PA ) close to the theoretical value at the unitarity limit. DOI:PACS number (s): 34.50.-s, 37.10.Mn, 33.20.-t Heteronuclear polar molecules have recently attracted enormous attention [1-17] owing to their ground state having a large electric dipole moment [16]. The long range anisotropic dipole-dipole interaction in such systems is the basis for a variety of applications including quantum computing [13], precision measurements [14], ultracold chemistry [2] and quantum simulations [15]. Heteronuclear bi-alkali molecules (XY, where X and Y are two different alkali atom species), 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 easily associated to form molecules at ultracold temperatures. The two primary methods for production of heteronuclear bialkali molecules have been magneto-association (MA), as in the case of KRb, NaK and NaLi [1][2][3][4], and photoassociation (PA), as in the case of LiCs, RbCs, NaCs, KRb and LiK [5][6][7][8][9][10][11][12]. Such molecules can be transferred to their absolute ground state where they have significant dipole moment, for example, by Stimulated Raman Adiabatic Passage (STIRAP) [1,12]. There is considerable interest in other heteronuclear combinations either due to their higher dipole moments, different quantum statistics or the possibility of finding simpler or more efficient methods for the production of ultracold molecules.In this Rapid Communication, we report a highly efficient production of ultracold 7 Li 85 Rb molecules by PA. Prior to our work (also see [18]), LiRb was one of the few bi-alkali molecules yet to be produced at ultracold temperatures. There is considerable interest in LiRb because the rovibronic ground state LiRb molecule is predicted to have a relatively high dipole moment of 4.1 Debye (exceeded only by LiCs and NaCs) [16], which makes it a strong candidate for many of the applications mentioned above. It is also interesting to note that bosonic 85 Rb, 87 Rb and 7 Li, and the fermionic 6 Li are among the more commonly trapped alkali atomic species. This can make LiRb molecules readily available in both fermionic and bosonic forms (depending on the Li isotope chosen), broadening the range of physics that can be studied. We provide the first step tow...
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 (MOT) apparatus, we detect PA resonances with binding energies up to ~62 cm -1 below the 7 Li 2s 2 S 1/2 + 85 Rb 5p 2 P 1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a 3 + state and excited electronic 3 3 and 4 3 + states, and identify a 3 + (v" = 7 -13), 3 3 (v ' = 0 -10) and 4 3 + (v ' = 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.
In this article, we report the measurement of collision-induced loss rate coefficients , Li Rb and , Rb Li , and also discuss means to significantly suppress such collision induced losses. We first describe our dual-species magneto-optical trap (MOT) that allows us to simultaneously trap ≥ 5×10 8 7 Li atoms loaded from a Zeeman slower and ≥ 2×10 8 85 Rb atoms loaded from a dispenser. We observe strong interspecies collision-induced losses in the MOTs which dramatically reduce the maximum atom number achievable in the MOTs. We measure the trap loss rate coefficients , Li Rb and , Rb Li , and, from a study of their dependence on the MOT parameters, determine the cause for the losses observed. Our results provide valuable insights into ultracold collisions between 7 Li and 85 Rb, guide our efforts to suppress collision induced losses, and also pave the way for the production of ultracold 7 Li 85 Rb molecules. DOI:PACS number(s): 34.50.-s, 37.10.De
We present spectra of ultracold 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 'n 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 ] £ + ground electronic state to either the B' n or the D 1 n electronic state that has been previously observed, with levels possibly as low as Y 1 E +(t>" = 2) being populated. We do not observe decay to weakly bound vibrational levels of the X ' E + or ai 'L+ electronic state in the spectra. We also deduce a lower bound of 3900 cm~' for the dissociation energy of the LiRb+ molecular ion.M uch attention has been given to cold polar m olecules [ 1,2] due to their potential as a m edium for precision m easurem ents [3][4][5], quantum com putation [6], quantum sim ulation [7], in vestigations o f tim e variation in fundam ental constants [8], and ultracold quantum chem istry [9,10]. E xperim ents that utilize the internal structure o f a m olecule can be conducted using m olecular ions or neutral m olecules. However, experim ents that seek to take advantage o f dipole-dipole interactions re quire an ultracold sam ple o f neutral polar m olecules [6], Their dipole m om ent, and thus interaction strength, is strongest in the rovibronic ground state. T he intrinsic lifetim e o f a m olecule in its ground state is infinite, m aking it an ideal quantum state for studies related to quantum inform ation, com putation, or sim ulation (in practice, however, the lifetim e is lim ited by the quality o f vacuum , depth o f the m olecular trap, etc.) So far, the m ost straightforw ard way to produce ultracold m olecules is through photoassociation (PA) or m agnetoassociation o f ultra cold atom s in a trap. PA involves inducing a scattering-bound transition via an optical field [11], w hile m agnetoassociation involves tuning an external m agnetic field to a Feshbach resonance [12]. Because alkali m etals have a single-valence electron and a strong cycling transition, they are com m only used in ultracold atom ic traps, and the m ost com m only studied ultracold m olecules are bialkalis. A m ong the bialkalis, LiRb is attractive due to its high PA rate (highest am ong the bialkalis [13,14]) and the large perm anent electric dipole m om ent in the rovibronic ground state (third highest am ong bialkalis [15]). U ltracold Li-Rb m ixtures are also a possible candidate for study o f a gas-crystal quantum transition [16,17]. However, until recently, LiRb was one o f the least experim entally studied bialkali m olecules. R ecent heat pipe spectra [18-20], m easurem ents o f large Feshbach reson...
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