Controlling collisions of ultracold atoms with dc electric fields

Diffuse Basis Functions for Relativistic s and d Block Gaussian Basis Sets

Diffuse s, p, and d functions have been optimized for use with previously reported relativistic basis sets for the s and d blocks of the periodic table. The functions were optimized on the 4:1 weighted average of the s² and p² configurations of the anion, with the d shell in the dⁿ⁺¹ configuration for the d blocks. Exponents were extrapolated for groups 2 and 12, which have unstable or weakly bound anions. The diffuse basis sets have been tested by application to calculations of electron affinities of the group 11 elements (Cu, Ag, and Au), double electron affinities of the group 11 monocations, and potential energy curves of Mg₂ and Ca₂ van der Waals dimers, as well as some response properties of the group 1 anions (Rb^-, Cs^-, and Fr^-), the group 2 elements (Sr, Ba, and Ra), and RbLi, CsLi, and FrLi molecules.

Channel Selection of Ultracold Atom-Molecule Scattering in Dynamic Magnetic Fields

We demonstrate that final states of ultracold molecules by scattering with atoms can be selectively produced using dynamic magnetic fields of multiple frequencies. We develop a multifrequency Floquet coupled channel method to study the channel selection by dynamic magnetic field control, which can be interpreted by a generalized quantum Zeno effect for the selected scattering channels. In particular, we use an atom-molecule spin-flip scattering to show that the transition to certain final states of the molecules in the inelastic scattering can be suppressed by engineered coupling between the Floquet states.

Non-Relativistic Electronic-Structure Computation of Neutral and Cationic Systems [Fr2, Fr-AEM+ (AEM= Ca, Sr, Ba)]

The experimental field of ultracold ion-atom mixtures including an alkali-metal atom and an alkaline-earth-metal ion as well as of homonuclear alkali dimers has paved the way for creating and manipulating the ultracold molecules. The present paper is focused on a study of molecules such us francium dimer and a comparative spectroscopic investigation of the cationic systems Fr-(Ca⁺, Sr⁺, Ba⁺). We adopt a computational scheme without spin-orbit coupling reposed on the full configuration interaction and semi-empirical pseudo-potential theory of the atomic cores Fr⁺, Ca²⁺, Sr²⁺, and Ba²⁺ with extended and optimized basis sets. We have determined the adiabatic potentials with their relative spectroscopic constants, the electric dipole moments and the vibrational levels spacings for the ^1,3Σ_u,g⁺ and ^1,3Σ⁺ electronic states for Fr₂ and Fr-AEM⁺, respectively, correlated toward {Fr(7s) + Fr(7s, 7p, 6d, 8s, 8p)}, {Ca(4s², 4s4p, 4s3d), Sr(5s², 5s5p, 5s4d), Ba(6s², 6s6p, 6s5d) + Fr⁺}, and {Ca⁺(4s, 3d), Sr⁺(5s, 4d), Ba⁺(6s, 5d) + Fr(7s, 7p)}. The accuracy and reliability of the current results are discussed by comparing with theoretical data available in the literature. The occurrence of some avoided crossings between the neighboring electronic states is leading to a charge or excitation transfer for atom-ion collisions in the diverse charge or excited states. The Σ⁺-Σ⁺ transitions are determined in order to evaluate the future radiative lifetimes of vibrational states serving the direct laser cooling.

Transparent electrodes for high E-field production using a buried indium tin oxide layer

We present a design and characterization of optically transparent electrodes suitable for atomic and molecular physics experiments where high optical access is required. The electrodes can be operated in air at standard atmospheric pressure and do not suffer electrical breakdown even for electric fields far exceeding the dielectric breakdown of air. This is achieved by putting an indium tin oxide coated dielectric substrate inside a stack of dielectric substrates, which prevents ion avalanche resulting from Townsend discharge. With this design, we observe no arcing for fields of up to 120 kV/cm. Using these plates, we directly verify the production of electric fields up to 18 kV/cm inside a quartz vacuum cell by a spectroscopic measurement of the dc Stark shift of the 5(2)S(1/2) → 5(2)P(3/2) transition for a cloud of laser cooled rubidium atoms. We also report on the shielding of the electric field and on the residual electric fields that persist within the vacuum cell once the electrodes are discharged. In addition, we discuss observed atom loss that results from the motion of free charges within the vacuum. The observed asymmetry of these phenomena on the bias of the electrodes suggests that field emission of electrons within the vacuum is primarily responsible for these effects and may indicate a way of mitigating them.

Theoretical study of the CsNa molecule: adiabatic and diabatic potential energy and dipole moment

The adiabatic and diabatic potential energy curves of the low-lying electronic states of the NaCs molecule dissociating into Na (3s, 3p) + Cs (6s, 6p, 5d, 7s, 7p, 6d, 8s, 4f) have been investigated. The molecular calculations are performed using an ab initio approach based on nonempirical pseudopotential, parametrized l-dependent polarization potentials and full configuration interaction calculations through the CIPCI quantum chemistry package. The derived spectroscopic constants (Re, De, Te, ωe, ωexe, and Be) of the ground state and lower excited states are compared with the available theoretical and experimental works. Moreover, accurate permanent and transition dipole moment have been determined as a function of the internuclear distance. The adiabatic permanent dipole moment for the first nine (1)Σ(+) electronic states have shown both ionic characters associated with electron transfer related to Cs(+)Na(-) and Cs(-)Na(+) arrangements. By a simple rotation, the diabatic permanent dipole moment is determined and has revealed a linear behavior, particularly at intermediate and large distances. Many peaks around the avoided crossing locations have been observed for the transition dipole moment between neighbor electronic states.

Controlling magnetic Feshbach resonances in polar open-shell molecules with nonresonant light

Magnetically tunable Feshbach resonances for polar paramagnetic ground-state diatomics are too narrow to allow for magnetoassociation starting from trapped, ultracold atoms. We show that nonresonant light can be used to engineer the Feshbach resonances in their position and width. For nonresonant field intensities of the order of 10(9) W/cm(2), we find the width to be increased by 3 orders of magnitude, reaching a few Gauss. This opens the way for producing ultracold molecules with sizable electric and magnetic dipole moments and thus for many-body quantum simulations with such particles.

Calculating and modeling the exchange energies of homonuclear and heteronuclear alkali dimers based on the surface integral method

The exchange energies of all homonuclear and heteronuclear alkali dimers are calculated based on the surface integral method. These results are generally in good agreement with both ab initio calculations and experimental results where available. It is also shown that the exchange energies could be fitted by an analytical expression of AR(b) exp(-cR). b and c can be calculated by two simple formulas that are only related to the ionization energies of the constituent atoms. A is the only parameter in this expression. More interestingly, it is found that the parameter A for the heteronuclear dimers could be approximated by a combining rule.

Molecular beam collisions with a magnetically trapped target

Cold, neutral hydroxyl radicals are Stark decelerated and efficiently loaded into a permanent magnetic trap. The OH molecules are trapped in the rovibrational ground state at a density of approximately 10;{6} cm;{-3} and temperature of 70 mK. Collision studies between the trapped OH sample and supersonic beams of atomic He and molecular D2 determine absolute collision cross sections. The He-OH and D2-OH center-of-mass collision energies are tuned from 60 cm;{-1} to 230 cm;{-1} and 145 cm;{-1} to 510 cm;{-1}, respectively, yielding evidence of quantum threshold scattering and resonant energy transfer between colliding particles.

Total control over ultracold interactions via electric and magnetic fields

The scattering length is commonly used to characterize the strength of ultracold atomic interactions, since it is the leading parameter in the low-energy expansion of the scattering phase shift. Its value can be modified via a magnetic field, by using a Feshbach resonance. However, the effective range term, which is the second parameter in the phase shift expansion, determines the width of the resonance and gives rise to important properties of ultracold gases. Independent control over this parameter is not possible by using a magnetic field only. We demonstrate that a combination of magnetic and electric fields can be used to get independent control over both parameters, which leads to full control over elastic ultracold interactions.

Magnetoelectrostatic trapping of ground state OH molecules

We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.

A Linear AC Trap for Polar Molecules in Their Ground State

A linear AC trap for polar molecules in high-field seeking states has been devised and implemented, and its characteristics have been investigated both experimentally and theoretically. The trap is loaded with slow 15ND3 molecules in their ground state (para-ammonia) from a Stark decelerator. The trap's geometry offers optimal access as well as improved loading. We present measurements of the dependence of the trap's performance on the switching frequency, which exhibit a characteristic structure due to nonlinear resonance effects. The molecules are found to oscillate in the trap under the influence of the trapping forces, which were analyzed using 3D numerical simulations. On the basis of expansion measurements, molecules with a velocity and a position spread of 2.1 m/s and 0.4 mm, respectively, are still accepted by the trap. This corresponds to a temperature of 2.0 mK. From numerical simulations, we find the phase-space volume that can be confined by the trap (the acceptance) to be 50 mm3 (m/s)3.

Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential

We discuss techniques to tune and shape the long-range part of the interaction potentials in quantum gases of bosonic polar molecules by dressing rotational excitations with static and microwave fields. This provides a novel tool towards engineering strongly correlated quantum phases in combination with low-dimensional trapping geometries. As an illustration, we discuss the 2D superfluid-crystal quantum phase transition for polar molecules interacting via an electric-field-induced dipole-dipole potential.

Manipulating spin-dependent interactions in rotationally excited cold molecules with electric fields

We use rigorous quantum mechanical theory to study collisions of magnetically oriented cold molecules in the presence of superimposed electric and magnetic fields. It is shown that electric fields suppress the spin-rotation interaction in rotationally excited 2Sigma molecules and inhibit rotationally elastic and inelastic transitions accompanied by electron spin reorientation. We demonstrate that electric fields enhance collisional spin relaxation in 3Sigma molecules and discuss the mechanisms for electric field control of spin-changing transitions in collisions of rotationally excited CaD(2Sigma) and ND(3Sigma) molecules with helium atoms. The propensities for spin depolarization in the rotationally excited molecules are analyzed based on the calculations of collision rate constants at T=0.5 K.

Suppression of quantum scattering in strongly confined systems

We demonstrate that scattering of particles strongly interacting in three dimensions (3D) can be suppressed at low energies in a quasi-one-dimensional (1D) confinement. The underlying mechanism is the interference of the s- and p-wave scattering contributions with large s- and p-wave 3D scattering lengths being a necessary prerequisite. This low-dimensional quantum scattering effect might be useful in "interacting" quasi-1D ultracold atomic gases, guided atom interferometry, and impurity scattering in strongly confined quantum wire-based electronic devices.

Mechanism and control of the F+H2 reaction at low and ultralow collision energies

This article uses theoretical methods to study the dependence on stereodynamical factors of the mechanism and reactivity of the F+H2 reaction at low and ultralow collision energies. The impact of polarization of the H2 reactant on total and state-to-state integral and differential cross sections is analyzed. This leads to detailed pictures of the reaction mechanism in the cold and ultracold regimes, accounting, in particular, for distinctions associated with the various product states and scattering angles. The extent to which selection of reactant polarization allows for external control of the reactivity and reaction mechanism is assessed. This reveals that even the simplest of reactant polarization schemes allows for fine, product state-selective control of differential and (for reactions involving more than a single, zero orbital angular momentum partial wave) integral cross sections.