Quantum scattering of icosahedron fullerene C with noble-gas atoms.

There exist multiple ways to cool neutral molecules. A front runner is the technique of buffer gas cooling, where momentum-changing collisions with abundant cold noble-gas atoms cool the molecules. This approach can, in principle, produce the most diverse samples of cold molecules.

Quantum Control of Atom-Ion Charge Exchange via Light-Induced Conical Intersections.

Conical intersections are crossing points or lines between two or more adiabatic electronic potential energy surfaces in the multidimensional coordinate space of colliding atoms and molecules. Conical intersections and corresponding nonadiabatic coupling can greatly affect molecular dynamics and chemical properties. In this paper, we predict significant or measurable nonadiabatic effects in an ultracold atom-ion charge-exchange reaction in the presence of laser-induced conical intersections (LICIs).

Signatures of Non-universal Quantum Dynamics of Ultracold Chemical Reactions of Polar Alkali Dimer Molecules with Alkali Metal Atoms: Li(S) + NaLi(Σ) → Na(S) + Li(Σ).

Ultracold chemical reactions of weakly bound triplet-state alkali metal dimer molecules have recently attracted much experimental interest. We perform rigorous quantum scattering calculations with a new potential energy surface to explore the chemical reaction of spin-polarized NaLi(Σ) and Li(S) to form Li(Σ) and Na(S). The reaction is exothermic and proceeds readily at ultralow temperatures.

Quantum Spin State Selectivity and Magnetic Tuning of Ultracold Chemical Reactions of Triplet Alkali-Metal Dimers with Alkali-Metal Atoms.

We demonstrate that it is possible to efficiently control ultracold chemical reactions of alkali-metal atoms colliding with open-shell alkali-metal dimers in their metastable triplet states by choosing the internal hyperfine and rovibrational states of the reactants as well as by inducing magnetic Feshbach resonances with an external magnetic field. We base these conclusions on coupled-channel statistical calculations that include the effects of hyperfine contact and magnetic-field-induced Zeeman interactions on ultracold chemical reactions of hyperfine-resolved ground-state Na and the triplet NaLi(a^{3}Σ^{+}) producing singlet Na_{2}(^{1}Σ_{g}^{+}) and a Li atom. We find that the reaction rates are sensitive to the initial hyperfine states of the reactants.

Realizing Hopf Insulators in Dipolar Spin Systems.

The Hopf insulator is a weak topological insulator characterized by an insulating bulk with conducting edge states protected by an integer-valued linking number invariant. The state exists in three-dimensional two-band models. We demonstrate that the Hopf insulator can be naturally realized in lattices of dipolar-interacting spins, where spin exchange plays the role of particle hopping.

Roaming pathways and survival probability in real-time collisional dynamics of cold and controlled bialkali molecules.

Perfectly controlled molecules are at the forefront of the quest to explore chemical reactivity at ultra low temperatures. Here, we investigate for the first time the formation of the long-lived intermediates in the time-dependent scattering of cold bialkali [Formula: see text]Rb molecules with and without the presence of infrared trapping light. During the nearly 50 nanoseconds mean collision time of the intermediate complex, we observe unconventional roaming when for a few tens of picoseconds either NaRb or [Formula: see text] and [Formula: see text] molecules with large relative separation are formed before returning to the four-atom complex.

Non-adiabatic quantum interference in the ultracold Li + LiNa → Li + Na reaction.

Electronically non-adiabatic effects play an important role in many chemical reactions. However, how these effects manifest in cold and ultracold chemistry remains largely unexplored. Here for the first time we present from first principles the non-adiabatic quantum dynamics of the reactive scattering between ultracold alkali-metal LiNa molecules and Li atoms.

Nondestructive dispersive imaging of rotationally excited ultracold molecules.

A barrier to realizing the potential of molecules for quantum information science applications is a lack of high-fidelity, single-molecule imaging techniques. Here, we present and theoretically analyze a general scheme for dispersive imaging of electronic ground-state molecules. Our technique relies on the intrinsic anisotropy of excited molecular rotational states to generate optical birefringence, which can be detected through polarization rotation of an off-resonant probe laser beam.

Effects of conical intersections on hyperfine quenching of hydroxyl OH in collision with an ultracold Sr atom.

The effect of conical intersections (CIs) on electronic relaxation, transitions from excited states to ground states, is well studied, but their influence on hyperfine quenching in a reactant molecule is not known. Here, we report on ultracold collision dynamics of the hydroxyl free-radical OH with Sr atoms leading to quenching of OH hyperfine states. Our quantum-mechanical calculations of this process reveal that quenching is efficient due to anomalous molecular dynamics in the vicinity of the conical intersection at collinear geometry.

Tune-Out and Magic Wavelengths for Ground-State ^{23}Na^{40}K Molecules.

We demonstrate a versatile, state-dependent trapping scheme for the ground and first excited rotational states of ^{23}Na^{40}K molecules. Close to the rotational manifold of a narrow electronic transition, we determine tune-out frequencies where the polarizability of one state vanishes while the other remains finite, and a magic frequency where both states experience equal polarizability. The proximity of these frequencies of only 10 GHz allows for dynamic switching between different trap configurations in a single experiment, while still maintaining sufficiently low scattering rates.

Photon-mediated charge exchange reactions between K atoms and Ca ions in a hybrid trap.

We present experimental evidence of charge exchange between laser-cooled potassium K atoms and calcium Ca ions in a hybrid atom-ion trap and give quantitative theoretical explanations for the observations. The K atoms and Ca ions are held in a magneto-optical (MOT) and a linear Paul trap, respectively. Fluorescence detection and high resolution time of flight mass spectra for both species are used to determine the remaining number of Ca ions, the increasing number of K ions, and K number density as functions of time.

Feshbach Resonances in -Wave Three-Body Recombination within Fermi-Fermi Mixtures of Open-Shell Li and Closed-Shell Yb Atoms.

We report on the observation of magnetic Feshbach resonances in a Fermi-Fermi mixture of ultracold atoms with extreme mass imbalance and on their unique -wave dominated three-body recombination processes. Our system consists of open-shell alkali-metal Li and closed-shell Yb atoms, both spin polarized and held at various temperatures between 1 and 20 K. We confirm that Feshbach resonances in this system are solely the result of a weak separation-dependent hyperfine coupling between the electronic spin of Li and the nuclear spin of Yb.

Engineering Excited-State Interactions at Ultracold Temperatures.

Using a recently developed method for precisely controlling collision energy, we observe a dramatic suppression of inelastic collisions between an atom and ion (Ca+Yb^{+}) at low collision energy. This suppression, which is expected to be a universal phenomenon, arises when the spontaneous emission lifetime of the excited state is comparable to or shorter than the collision complex lifetime. We develop a technique to remove this suppression and engineer excited-state interactions.

Extending Rotational Coherence of Interacting Polar Molecules in a Spin-Decoupled Magic Trap.

Superpositions of rotational states in polar molecules induce strong, long-range dipolar interactions. Here we extend the rotational coherence by nearly 1 order of magnitude to 8.7(6) ms in a dilute gas of polar ^{23}Na^{40}K molecules in an optical trap.

Pendular trapping conditions for ultracold polar molecules enforced by external electric fields.

We theoretically investigate trapping conditions for ultracold polar molecules in optical lattices, when external magnetic and electric fields are simultaneously applied. Our results are based on an accurate electronic-structure calculation of the polar NaK polar molecule in its absolute ground state combined with a calculation of its rovibrational-hyperfine motion. We find that an electric field strength of 5.

Fractal universality in near-threshold magnetic lanthanide dimers.

Ergodic quantum systems are often quite alike, whereas nonergodic, fractal systems are unique and display characteristic properties. We explore one of these fractal systems, weakly bound dysprosium lanthanide molecules, in an external magnetic field. As recently shown, colliding ultracold magnetic dysprosium atoms display a soft chaotic behavior with a small degree of disorder.

Orbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms.

Laser-cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces.

Laser controlled charge-transfer reaction at low temperatures.

We study the low-temperature charge transfer reaction between a neutral atom and an ion under the influence of near-resonant laser light. By setting up a multi-channel model with field-dressed states, we demonstrate that the reaction rate coefficient can be enhanced by several orders of magnitude with laser intensities of 10 W/cm or larger. In addition, depending on laser frequency, one can induce a significant enhancement or suppression of the charge-exchange rate coefficient.

Explanation of efficient quenching of molecular ion vibrational motion by ultracold atoms.

Buffer gas cooling of molecules to cold and ultracold temperatures is a promising technique for realizing a host of scientific and technological opportunities. Unfortunately, experiments using cryogenic buffer gases have found that although the molecular motion and rotation are quickly cooled, the molecular vibration relaxes at impractically long timescales. Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl(+) by a laser-cooled Ca buffer gas.

Photodissociation spectroscopy of the dysprosium monochloride molecular ion.

We have performed a combined experimental and theoretical study of the photodissociation cross section of the molecular ion DyCl(+). The photodissociation cross section for the photon energy range 35,500 cm(-1) to 47,500 cm(-1) is measured using an integrated ion trap and time-of-flight mass spectrometer; we observe a broad, asymmetric profile that is peaked near 43,000 cm(-1). The theoretical cross section is determined from electronic potentials and transition dipole moments calculated using the relativistic configuration-interaction valence-bond and coupled-cluster methods.

Controlling interactions between highly magnetic atoms with Feshbach resonances.

This paper reviews current experimental and theoretical progress in the study of dipolar quantum gases of ground and meta-stable atoms with a large magnetic moment. We emphasize the anisotropic nature of Feshbach resonances due to coupling to fast-rotating resonant molecular states in ultracold s-wave collisions between magnetic atoms in external magnetic fields. The dramatic differences in the distribution of resonances of magnetic (7)S3 chromium and magnetic lanthanide atoms with a submerged 4f shell and non-zero electron angular momentum is analyzed.

Action spectroscopy of SrCl⁺ using an integrated ion trap time-of-flight mass spectrometer.

The photodissociation cross-section of SrCl(+) is measured in the spectral range of 36,000-46,000 cm(-1) using a modular time-of-flight mass spectrometer (TOF-MS). By irradiating a sample of trapped SrCl(+) molecular ions with a pulsed dye laser, X(1)Σ(+) state molecular ions are electronically excited to the repulsive wall of the A(1)Π state, resulting in dissociation. Using the TOF-MS, the product fragments are detected and the photodissociation cross-section is determined for a broad range of photon energies.

Quantum chaos in ultracold collisions of gas-phase erbium atoms.

Atomic and molecular samples reduced to temperatures below one microkelvin, yet still in the gas phase, afford unprecedented energy resolution in probing and manipulating the interactions between their constituent particles. As a result of this resolution, atoms can be made to scatter resonantly on demand, through the precise control of a magnetic field. For simple atoms, such as alkalis, scattering resonances are extremely well characterized.

Ultracold heteronuclear mixture of ground and excited state atoms.

We report on the realization of an ultracold mixture of lithium atoms in the ground state and ytterbium atoms in an excited metastable (3P2) state. Such a mixture can support broad magnetic Feshbach resonances which may be utilized for the production of ultracold molecules with an electronic spin degree of freedom, as well as novel Efimov trimers. We investigate the interaction properties of the mixture in the presence of an external magnetic field and find an upper limit for the background interspecies two-body inelastic decay coefficient of K2'<3×10(-12)  cm3/s for the 3P2 mJ=-1 substate.