LiCs Molecules Research Articles

Ab initio study of R-dependent behavior of the hyperfine structure parameters for the [formula omitted] states of LiRb and LiCs

Diagonal a3Σ1+-a3Σ1+ and off–diagonal X1Σ0++-a3Σ0-+ magnetic hyperfine structure (HFS) matrix elements were calculated ab initio for the LiRb and LiCs molecules in a wide range of internuclear distances using the multi–reference Fock space coupled clusters method with generalized relativistic effective core potentials to describe the four–component valence wavefunctions near the nuclei. At large distances, both HFS functions vary little, though they may fluctuate by as much as 12 to 24% in the intermediate range. The plateau exhibited by the a3Σ1+-a3Σ1+ HFS function at 4–5 Å, could be attributed to pronounced spin–orbit coupling of the intersecting a3Σ+ and b3Π states.

Formation and vibrational stabilization of cold heteronuclear molecules by a single infrared pulse with time-dependent frequency

We consider the formation and vibrational stabilization of cold heteronuclear molecules using infrared nanosecond pulses. Starting with a pair of colliding cold atoms of dissimilar species, our objective is the formation of a molecule in its electronic and vibrational ground level by means of the interaction with the laser field. In order to meet this goal, we propose the employment of a single pulse with a time-dependent frequency following a predefined transition pathway. We show that the proposed scheme can efficiently form cold molecules in the vibrational ground level. Calculations are performed for a model representing the formation of LiCs molecules in the milikelvin temperature range.

Coherent control of the formation of cold heteronuclear molecules by photoassociation

We consider the formation of cold diatomic molecules in the electronic ground state by photoassociation of atoms of dissimilar species. A combination of two transition pathways from the free colliding pair of atoms to a bound vibrational level of the electronic molecular ground state is envisioned. The first pathway consists of a pump-dump scheme with two time-delayed laser pulses in the near-infrared frequency domain. The pump pulse drives the transition to a bound vibrational level of an excited electronic state, while the dump pulse transfers the population to a bound vibrational level of the electronic ground state. The second pathway takes advantage of the existing permanent dipole moment and employs a single pulse in the far-infrared domain to drive the transition from the unbound atoms directly to a bound vibrational level in the electronic ground state. We show that this scheme offers the possibility to coherently control the photoassociation yield by manipulating the relative phase and timing of the pulses. The photoassociation mechanism is illustrated for the formation of cold LiCs molecules.

Observation of interspecies6Li-133Cs Feshbach resonances

We report on the observation of nineteen interspecies Feshbach resonances in an optically trapped ultracold Bose-Fermi mixture of ^{133}Cs and ^{6}Li in the two energetically lowest spin states. We assign the resonances to s- and p-wave molecular channels by a coupled-channels calculation, resulting in an accurate determination of LiCs ground state potentials. Fits of the resonance position based on the undressed Asymptotic Bound State model do not provide the same level of accuracy as the coupled-channels calculation. Several broad s-wave resonances provide prospects to create fermionic LiCs molecules with a large dipole moment via Feshbach association followed by stimulated Raman passage. Two of the s-wave resonances overlap with a zero crossing of the Cs scattering length which offers prospects for the investigation of polarons in an ultracold Li-Cs mixture.

Population redistribution in optically trapped polar molecules

We investigate the rovibrational population redistribution of polar molecules in the electronic ground state induced by spontaneous emission and blackbody radiation. As a model system we use optically trapped LiCs molecules formed by photoassociation in an ultracold two-species gas. The population dynamics of vibrational and rotational states is modeled using an ab initio electric dipole moment function and experimental potential energy curves. Comparison with the evolution of the v″ = 3 electronic ground state yields good qualitative agreement. The analysis provides important input to assess applications of ultracold LiCs molecules in quantum simulation and ultracold chemistry.

The X 1Σ+ state of LiRb studied by Fourier-transform spectroscopy

We report on the first experimental observation of the ground electronic state of the LiRb molecule at high resolution. A large body of experimental data was collected which led to an accurate potential energy curve for this state. Transitions to the lowest triplet state were also observed, but these data are rather fragmentary and allow only a first attempt for the description of this state. Both potentials were used for evaluating published Feshbach resonances of this molecule. We compare the results of this study with those of the related LiK and LiCs molecules.

Dipolar effects and collisions in an ultracold gas of LiCs molecules

We review our recent experiments on the formation and optical trapping of LiCs molecules, which are photoassociated from a mixed ultracold gas of Li and Cs atoms. The electric dipole moment of the atoms in the lowest vibrational states is measured, yielding the predicted value of 5.5 Debye, and vibrational redistribution due to spontaneous emission and blackbody radiation is observed. We also show preliminary results on inelastic collision between optically trapped LiCs molecules and Cs atoms.

Inelastic collisions of ultracold polar LiCs molecules with caesium atoms in an optical dipole trap

We investigate collisions of ultracold polar LiCs molecules and ultracold caesium atoms. LiCs molecules are formed in an optical dipole trap by photoassociation of caesium and lithium atoms via the B(1)Π excited state followed by spontaneous emission to the X(1)Σ(+) ground state and the lowest triplet state a(3)Σ(+). The molecules are then stored together with caesium atoms in the same optical trap. Rate coefficients for the loss of molecules induced by collisions with surrounding Cs atoms are measured for molecular ensembles produced via different photoassociation resonances. The results are analyzed in terms of the unitarity limit for the inelastic rates and predictions from the universal model of Idziaszek and Julienne (Phys. Rev. Lett., 2010, 104, 113202).

Permanent dipole moment of LiCs in the ground state

Recently we demonstrated the formation of ultracold polar LiCs molecules in deeply bound levels of the X1S+ ground state, including the rovibrational ground state [J. Deiglmayr et al., Phys. Rev. Lett. 101, 133004 (2008)]. Here we report on the first experimental determination of the permanent electric dipole moment of deeply bound LiCs molecules. For X1S+,v"=2 and v"=3 we measure values of mu=5.5(2) Debye and 5.3(2) Debye respectively.

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

We recently reported the formation of ultracold LiCs molecules in the rovibrational ground state X1sigma+, v" = 0,J" = 0 (J. Deiglmayr et al., Phys. Rev. Lett., 2008, 101, 133004). 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 X1sigma+ state by high resolution spectroscopy of the vibrational ground state.

Formation of Ultracold Polar Molecules in the Rovibrational Ground State

Ultracold LiCs molecules in the absolute ground state X1Sigma+, v'' = 0, J'' = 0 are formed via a single photoassociation step starting from laser-cooled atoms. The selective production of v'' = 0, J'' = 2 molecules with a 50-fold higher rate is also demonstrated. The rotational and vibrational state of the ground state molecules is determined in a setup combining depletion spectroscopy with resonant-enhanced multiphoton ionization time-of-flight spectroscopy. Using the determined production rate of up to 5 x 10(3) molecules/s, we describe a simple scheme which can provide large samples of externally and internally cold dipolar molecules.

Formation of ultracold LiCs molecules

We present the first observation of ultracold LiCs molecules. The molecules are formed in a two-species magneto-optical trap and detected by two-photon ionization and time-of-flight mass spectrometry. The production rate coefficient is found to be in the range 10−18 cm3 s−1 to 10−16 cm3 s−1, at least an order of magnitude smaller than for other heteronuclear diatomic molecules directly formed in a magneto-optical trap.