Formation of ultracold LiRb molecules by photoassociation near the Li(2 s   ² S _1/2 ) + Rb(5 p   ² P _1/2 ) asymptote

Abstract

-We report the production of ultracold 7 Li 85 Rb molecules by photoassociation (PA) below the Li (2s 2 S 1/2 ) + Rb (5p 2 P 1/2 ) asymptote. We perform PA spectroscopy in a dual-species 7 Li-85 Rb magneto-optical trap (MOT) and detect the PA resonances using trap loss spectroscopy. We observe several strong PA resonances corresponding to the last few bound states, assign the lines and derive the long range C 6 dispersion coefficients for the Li (2s 2 S 1/2 ) + Rb (5p 2 P 1/2 ) asymptote. We also report an excited-state molecule formation rate (P LiRb ) of ~10 7 s -1 and a PA rate coefficient (K PA ) of ~4×10 -11 cm 3 /s, which are both among the highest observed for heteronuclear bi-alkali molecules. These suggest that PA is a promising route for the creation of ultracold ground state LiRb molecules.

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

“…Through earlier traploss measurements, we identified PA lines up to u PA = 4 for 2(0 + ), and u PA = 5 for 2(0 -) and 2(1) [17].…”

Two-photon photoassociation spectroscopy of an ultracold heteronuclear molecule

“…2(a) we show an example of the 1-photon PA spectrum of the level of the 2(1) state when the PA laser is scanned in the absence of the Raman laser (negative sign in denotes that the level is measured from the dissociation limit). For the Ramantype 2-photon PA spectroscopy, the frequency PA 1.7 GHz are due to 1-photon PA transitions induced by the Raman laser -the first three corresponds to the 2(1), level, while the last corresponds to the 2(0 -), level [10]. We now discuss assignments for some of the observed 2-photon PA spectra of 7 Li 85 Rb.…”

“…The frequency PA  of the PA laser is tuned to at a PA transition to create LiRb* molecules in a specific bound vibrational level near the Li (2s 2 S 1/2 ) + Rb (5p 2 P 1/2 ) atomic asymptote (* indicates electronically excited states). Molecule production leads to a reduction in the number of atoms trapped in the MOT and a corresponding reduction in atomic fluorescence [10,11]. We show an example of this trap loss signal in Fig.…”

“…The implication of this observation on direct atom to molecule conversion using stimulated Raman adiabatic passage (STIRAP) is discussed and the prospect for electronic ground state molecule production is theoretically analyzed. There has been immense interest and progress in creating ultracold heteronuclear polar molecules [1][2][3][4][5][6][7][8][9][10][11][12] which, by virtue of their permanent electric dipole moment in the electronic ground state, are important for a variety of experiments not possible with ultracold atoms [13][14][15][16]. One-photon photoassociation (PA) of ultracold atoms [17] has been extensively used to create ultracold diatomic molecules in excited electronic states [12] and in many cases such molecules spontaneously decay to the electronic ground state [3,[18][19][20][21][22].…”

“…In our case N sc = 0 since primarily s-wave scattering is possible at the sub mK temperatures of the MOTs [10,11], restricting Nʺ to 0 or 2. The observation (see Table I) of the Nʺ = 0 and Nʺ = 2 rotational levels of the X 1 Σ + ( = 51) state confirms the selection rule and the predominance of s-wave collisions.…”