High-resolution photoassociation spectroscopy of the6Li2A(11

Abstract

We present spectroscopic measurements of seven vibrational levels v = 29-35 of the A(1 1 + u ) excited state of Li 2 molecules by the photoassociation of a degenerate Fermi gas of 6 Li atoms. The absolute uncertainty of our measurements is ±0.000 02 cm −1 (±600 kHz) and we use these new data to further refine an analytic potential for this state. This work provides high accuracy photoassociation resonance locations essential for the eventual high-resolution mapping of the X(1 1 + g ) state enabling further improvements to the s-wave scattering length determination of Li and enabling the eventual creation of ultracold ground-state 6 Li 2 molecules.Since the development of laser cooling techniques for atoms, photoassociation spectroscopy (PAS) has been used to make precise measurements of molecular vibrational levels including very weakly bound states that are difficult to access with traditional bound-bound molecular spectroscopy. The precision of these types of measurements is due in large part to the extremely low ensemble temperatures achievable with laser cooling. At sufficiently low temperatures the collision energy is so small that the inhomogeneous broadening of the spectral lines can be negligible compared to the natural linewidth. In addition, cold atomic ensembles can be confined in a very weak optical dipole trap providing extremely long interrogation times and exceedingly small ac Stark shifts from both the confining laser light and the photoassociation light. Singlecolor PAS of excited molecular states has allowed for accurate determinations of atomic lifetimes and two-color PAS of ground molecular states has enabled the precise determination of atom-atom scattering lengths and the production of ultracold molecules as discussed in several excellent review articles [1][2][3][4][5].In this work, we measure the binding energies of seven vibrational levels v = 29-35 of the A(1 1 + u ) excited state of 6 Li 2 molecules with an absolute uncertainty of ±0.000 02 cm −1 (±600 kHz) by photoassociating a quantum degenerate Fermi gas of lithium atoms held in a shallow optical dipole trap. These measurements represent an observation of the N = 1 rotational level for each of the reported vibrational levels. These measurements compliment previous measurements of various ro-vibrational levels in the range v = 0-88 [6-11], while having absolute uncertainties that are 25 to 500 times smaller.This measurement is part of a larger project to characterize the excited A(1 1 + u ) (this paper) and c(1 3 + g ) [12] molecular levels of 6 Li 2 , as well as the ground spin-singlet X(1 1 + g ) and lowest lying spin-triplet a(1 3 + u ) potentials. In particular, this work is motivated by several factors. First, the levels measured in this work can serve as convenient intermediate states for a high resolution study of the X(1 1 + g ) state which is unexplored in the ultracold regime, with the exception of experiments involving Feshbach molecules created using the narrow 6 Li Feshbach resonance near 543 G, resulting from the v = 38 ...

LEVEL: A computer program for solving the radial Schrödinger equation for bound and quasibound levels

“…(20), but could take on any form predicted by theory. In particular, in the present version of LEVEL it may be represented as one of the roots of a 2 Â 2 or 3 Â 3 diagonalization arising from the type of two-state [33,49] or three-state [50,51] coupling encountered for alkali dimers at the first nS þnP asymptote [44]. A more detailed discussion of various features of the MLR potential function forms may be found in Ref.…”

An adaptable dual species effusive source and Zeeman slower design demonstrated with Rb and Li

“…Having dispensers or atomic ovens close to the trapping region can result in higher background pressures that limit the trap lifetime and thus the achievable atom number in the MOT [41,42]. However, such an approach has proven successful in the production of degenerate gases of 6 Li [43]. By placing the atomic oven further away from the trapping region, differential pumping techniques can be used to reduce the contribution of the background pressure in the trapping region due to the hot atomic sources.…”

“…Second, the decreasing magnetic field of the slower can be mated with the magnetic field from the quadrupole coils of the MOT such that the slower length can be made significantly shorter as the atoms complete the final stage of slowing after entering the MOT trapping region. Using the MOT field to provide slowing has been used in our previous experimental apparatus [43] and in similar dual species slowers [29].…”

All-optical production and transport of a largeLi6quantum gas in a crossed optical dipole trap

“…To increase the visibility of the bimodal density distribution, which is characteristic for the onset of Bose-Einstein condensation, the interaction strength between the molecules is lowered by linearly reducing the magnetic field to 690 G in 100 ms before TOF absorption imaging [6,31]. This reduces the atomic scattering length a 12 to around 1400 a 0 , which is related to the molecular s-wave scattering length via a mol = 0.6 a 12 [32].…”