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arXiv:1404.1255 · Physical Review Letters

Probing the Axis Alignment of an Ultracold Spin-polarized Rb2 Molecule

Markus Deiß, Björn Drews, Benjamin Deissler, Johannes Hecker Denschlag

Published Dec 3, 2014• 20 citations
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Abstract

We present a novel method for probing the alignment of the molecular axis of an ultracold, nonpolar dimer. These results are obtained using diatomic ^{87}Rb_{2} molecules in the vibrational ground state of the lowest triplet potential a^{3}Σ_{u}^{+} trapped in a 3D optical lattice. We measure the molecular polarizabilities, which are directly linked to the alignment, along each of the x, y, and z directions of the lab coordinate system. By preparing the molecules in various, precisely defined rotational quantum states we can control the degree of alignment of the molecular axis with high precision over a large range. Furthermore, we derive the dynamical polarizabilities for a laser wavelength of 1064.5 nm parallel and orthogonal to the molecular axis of the dimer, α_{∥}=(8.9±0.9)×10^{3} a.u. and α_{⊥}=(0.9±0.4)×10^{3} a.u., respectively. Our findings highlight that the depth of an optical lattice strongly depends on the rotational state of the molecule, which has to be considered in collision experiments. The present work paves the way for reaction studies between aligned molecules in the ultracold temperature regime.

DOI
10.1103/physrevlett.113.233004

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Probing the alignment of ultracold spin-polarized Rb2\textrm{Rb}_2Rb2​ molecules
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Abstract We study, both theoretically and experimentally, the dynamical polarizability of molecules in the rovibrational ground state of . Taking all relevant excited molecular bound states into account, we compute the complex-valued polarizability for wave numbers up to 20 000 . Our calculations are compared to experimental results at ( ) as well as at ( ). Here, we discuss the measurements at . The ultracold Rb2 molecules are trapped in the lowest Bloch band of a 3D optical lattice. Their polarizability is determined by lattice modulation spectroscopy which measures the potential depth for a given light intensity. Moreover, we investigate the decay of molecules in the optical lattice, where lifetimes of more than are observed. In addition, the dynamical polarizability for the state is calculated. We provide simple analytical expressions that reproduce the numerical results for for all vibrational levels of as well as . Precise knowledge of the molecular polarizability is essential for designing experiments with ultracold molecules as lifetimes and lattice depths are key parameters. Specifically the wavelength at is of interest, since here, ultrastable high power lasers are available.
We report the measurement of the anisotropic ac polarizability of ultracold polar (40)K(87)Rb molecules in the ground and first rotationally excited states. Theoretical analysis of the polarizability agrees well with experimental findings. Although the polarizability can vary by more than 30%, a "magic" angle between the laser polarization and the quantization axis is found where the polarizability of the |N=0,m(N)=0> and the |N=1,m(N)=0> states match. At this angle, rotational decoherence due to the mismatch in trapping potentials is eliminated, and we observe a sharp increase in the coherence time. This paves the way for precise spectroscopic measurements and coherent manipulations of rotational states as a tool in the creation and probing of novel quantum many-body states of polar molecules.
The rapid development of experimental techniques to produce ultracold alkali molecules opens the ways to manipulate them and to control their dynamics using external electric fields. A prerequisite quantity for such studies is the knowledge of their static dipole polarizability. In this paper, we computed the variations with internuclear distance and with vibrational index of the static dipole polarizability components of all homonuclear alkali dimers including Fr(2), and of all heteronuclear alkali dimers involving Li to Cs, in their electronic ground state and in their lowest triplet state. We use the same quantum chemistry approach as in our work on dipole moments [Aymar and Dulieu, J. Chem. Phys. 122, 204302 (2005)], based on pseudopotentials for atomic core representation, Gaussian basis sets, and effective potentials for core polarization. Polarizabilities are extracted from electronic energies using the finite-field method. For the heaviest species Rb(2), Cs(2), and Fr(2) and for all heteronuclear alkali dimers, such results are presented for the first time. The accuracy of our results on atomic and molecular static dipole polarizabilities is discussed by comparing our values with the few available experimental data and elaborate calculations. We found that for all alkali pairs, the parallel and perpendicular components of the ground state polarizabilities at the equilibrium distance R(e) scale as (R(e))(3), which can be related to a simple electrostatic model of an ellipsoidal charge distribution. Prospects for possible alignment and orientation effects with these molecules in forthcoming experiments are discussed.
Abstract Exploring and controlling inelastic and reactive collisions on the quantum level is a main goal of the developing field of ultracold chemistry. For this, the preparation of precisely defined initial atomic and molecular states in tailored environments is necessary. Here we present experimental studies of inelastic collisions of metastable ultracold Rb2 molecules in an array of quasi-1D potential tubes. In particular, we investigate collisions of molecules in the absolute lowest triplet energy level where any inelastic process requires a change of the electronic state. Remarkably, we find similar decay rates as for collisions between rotationally or vibrationally excited triplet molecules where other decay paths are also available. The decay rates are close to the ones for universal reactions but vary considerably when confinement and collision energy are changed. This might be exploited to control the collisional properties of molecules.