Formation of ultracold dipolar molecules in the lowest vibrational levels by photoassociation

Abstract

We recently reported the formation of ultracold LiCs molecules in the rovibrational ground state et al., PRL 101, 133004 (2008)]. Here we discuss details of the experimental setup and present a thorough analysis of the photoassociation step including the photoassociation line shape. We predict the distribution of produced ground state molecules using accurate potential energy curves combined with an ab-initio dipole transition moment and compare this prediction with experimental ionization spectra. Additionally we improve the value of the dissociation energy for the X 1 Σ + state by high resolution spectroscopy of the vibrational ground state.

Permanent dipole moment of LiCs in the ground state

“…Then depletion spectroscopy of v = 2, J = 0 and v = 3, J = 0 is performed in electric fields varying from 0 to 488 V/cm. We did not obtain depletion spectra with sufficient signal to noise ratio for Stark spectroscopy from the J = 0 component of 2 Due to thermal broadening the PA resonances are significantly broader than the depletion resonances [5], which were found to be around 30 MHz at zero field.…”

“…In this configuration 4 × 10 7 133 Cs and 10 8 7 Li atoms are trapped simultaneously at densities of 3 × 10 9 cm −3 and 10 10 cm −3 and temperatures of 250(50) µK and 600(150) µK respectively. Details of the experimental setup for the formation and detection of ultracold LiCs molecules have been given elsewhere [5,6,10]. For PA of LiCs molecules the two overlapped atom clouds are continuously illuminated by light from a tunable cw Ti:sapphire laser (typically 500 mW, collimated to 1.0 mm).…”

“…LiCs is predicted to have the largest permanent electric dipole moment (EDM) of all alkali-metal dimers [4] and is thus very advantageous for such schemes. Recently we have reported the formation of LiCs molecules in deeply bound levels of the X 1 + ground state [5], including the rovibrational ground state [6], after a single step of photoassociation (PA). Here we report on an experimental determination of the permanent EDM of deeply bound LiCs molecules.…”

Ultracold Polar Molecules in the Rovibrational Ground State

“…22 Analyzing the thermal broadening of a PA resonance without hyperfine structure, we find the best fit between experiment and model for collision energies corresponding to a temperature of T =580(80)μK. 16 This relatively high temperature has to be seen in relation to the centrifugal barrier E for collisions with higher angular momentum : for p-wave scattering the barrier is E =1 =1.6mK, and for d-wave scattering E =2 =8.5mK. Our measured collision energy is well below the p-wave limit, so that one can expect to observe dominantly s-wave scattering.…”

“…For heteronuclear dimers, the spontaneous decay following photoassociation of bound excited molecular states from free pairs of atoms mainly populates bound states of the electronic ground state, in contrast to the case of homonuclear dimers. 16 Subsequent resonantly enhanced multi-photon ionization is used to state-sensitively detect of the ultracold molecules. A schematic view of the relevant processes and the molecular levels involved is shown in Fig.…”