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.

We observe two consecutive heteronuclear Efimov resonances in an ultracold Li-Cs mixture by measuring three-body loss coefficients as a function of magnetic field near a Feshbach resonance. The first resonance is detected at a scattering length of a (0) − = −320(10) a0 corresponding to ∼ 7(∼ 3) times the Li-Cs (Cs-Cs) van der Waals range. The second resonance appears at 5.8(1.0) a (0) − close to the unitarity-limited regime at the sample temperature of 450 nK. Indication of a third resonance is found in the atom loss spectra. The scaling of the resonance positions is close to the predicted universal scaling value of 4.9 for zero temperature. Deviations from universality might be caused by finite-range and temperature effects, as well as magnetic field dependent Cs-Cs interactions.The control of interactions in ultracold atomic systems via magnetically tunable Feshbach resonances opens up new pathways for the investigation of few-and manybody physics [1]. One intriguing example is the access to the universal regime, which is characterized by a magnitude of the scattering length a exceeding all other length scales of the system. In the limit of at least two resonant pairwise interactions, an infinite series of three-body bound-states, the so called Efimov states, exists [2][3][4]. Counterintuitively, these trimers persist even for a < 0, where the two body potential does not support a boundstate. The ratio between two subsequent trimer energies follows a discrete scale invariance with a universal scaling factor of exp(−2π/s 0 ). Here, s 0 only depends on the quantum statistics of the constituent atoms, their mass ratio, and the number of resonant interactions [3, 5]. This scale invariance is also reflected in those values of a where the energy of the bound-states coincides with the threshold of three free atoms for a < 0, resulting in enhanced three-body loss. When the position of the first resonance is given by a − only depends on the characteristic range r 0 of the interatomic van der Waals potential [6][7][8][9][10][11]. The universal scaling factor acquires a value of 22.7 for equal mass constituents and features a drastic reduction in heteronuclear massimbalanced systems of two heavy and one light particle [3, 5], resulting e.g. in a factor of 4.9 for a 6 Li-133 Cs mixture.In ultracold atom experiments, Efimov resonances become evident in the three-body loss coefficient L 3 in the rate equation for atom lossṅ = −L 3 n 3 . Here, n denotes the number density of atoms, and L 3 ∝ C(a)a 4 . The Efimov physics are contained in the dimensionless, logperiodic function C(a). Thus far, Efimov resonances have been studied in several equal mass systems [6,7,[12][13][14][15][16][17][18], where the scaling between different resonances is predicted to follow C(a) = C(22.7a). This large scaling factor demands a level of temperature and magnetic field control which makes the observation of an excited Efimov states highly involved. There had been indication of such an excited state in a three-component Fermi gas of 6 Li atoms ...

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. [4][5][6], which gives access to the study of many-body physics, quantum chemistry and precision measurements [7,8]. With a permanent electric dipole moment of 5.5 Debye [9,10], the largest among all alkali-metal dimers, a system of LiCs molecules in their energetically lowest states [11] is considered to be an excellent candidate for the investigation of dipolar quantum gases [12]. Another application of the precise tunability close to a FR is the study of Efimov trimers [13]. The large mass ratio of m Cs /m Li = 22 results in an advantageous universal scaling factor of 4.88 instead of 22.7 as found for a system of equal masses [14], resulting in excellent conditions for observing a series of several Efimov resonances, which, so far, has not been achieved. Interspecies FR can be also used to control the interaction between an impurity and a Bose-Einstein Condensate (BEC). Such a system can directly be mapped to the Fröhlich polaron Hamiltonian [15][16][17], which describes the interaction of an electron gas with the charged lattice atoms in a crystal. As the excitations in a Bose-Einstein condensate represent the lattice phonons, a FR allows the precise adjustment of the modeled phonon-electron coupling strength α, thus allowing one to explore fundamental solid-state systems.FRs between different alkaline species have been identified for a variety of Bose-Bose [18][19][20][21] Cs were studied by means of thermalization measurements at zero magnetic field [40], however, the tunability of the interspecies scattering properties via tuning the magnetic field has yet remained unexplored. Here, we report on the observation of nineteen interspecies loss features in different spin channels of an optically trapped 6 Li -133 Cs mixture, by scanning a homogeneous magnetic field (Feshbach spectroscopy). The magnetic field positions and widths of the observed FRs are analyzed in a full coupled-channels calculation, allowing a consistent assignment of the resonances.We have realized an all-optical preparation scheme to simultaneously trap an ultracold 6 Li -133 Cs mixture with a magnetic field control up to 1300 G by sequentially transferring Li and Cs atoms into an optic...

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We provide a comprehensive comparison of a coupled channel calculation, the asymptotic bound-state model (ABM), and the multichannel quantum defect theory (MQDT (2013)]. We demonstrate how the accuracy of the ABM can be stepwise improved by including magnetic dipole-dipole interactions and coupling to a nondominant virtual state. We present a MQDT calculation, where magnetic dipole-dipole and second-order spin-orbit interactions are included. A frame transformation formalism is introduced, which allows the assignment of measured FRs with only three parameters. All three models achieve a total rms error of <1 G on the observed FRs. We critically compare the different models in view of the accuracy for the description of FRs and the required input parameters for the calculations.

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).

Recently we demonstrated the formation of ultracold polar LiCs molecules in deeply bound levels of the X 1 + ground state, including the rovibrational ground state [J. Deiglmayr et al., Phys. Rev. Lett. 101, 133004 (2008)].Here we report on an experimental determination of the permanent electric dipole moment of deeply bound LiCs molecules. For X 1 + , v = 2, and v = 3 we measure values of µ = 5.5(2) D and 5.3(2) D, respectively.

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.