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A new twist on Feshbach resonances: heteronuclear atomic mixtures in combined electric and magnetic fields

Kirk W. Madison

Published Jan 1, 2012• 0 citations
OpenAlex

Abstract

can be tuned using an external magnetic field. When the energy of the quasi-bound state is magnetically tuned into degeneracy with the energy of the free atomic pair, a resonant scattering process occurs in which the s-wave scattering length diverges and both elastic and inelastic collision cross sections are dramatically enhanced. When the collision involves two distinct atoms, the underlying molecular states can possess an electric dipole moment. In this case, the application of an external electric field can couple the bound molecular states mixing their orbital character and leading to level repulsion which breaks the degeneracy for dierent orbital angular momentum projections. The result is that the electric field shifts the positions of intrinsic magnetic Feshbach resonances, generates copies of resonances previously restricted to a particular partial-wave collision to other partial-wave channels, and splits Feshbach resonances into multiple resonances for states of nonzero angular momenta. This latter phenomenon oers a way to produce and tune an anisotropic interaction in atomic mixtures and to produce p-wave molecules of particular orbital angular momenta projections (1). In this talk, we discuss recent theoretical work and experimental progress on the realization and study of these phenomena associated with electric field dressing of magnetically tunable Feshbach resonances.

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can be tuned using an external magnetic field. When the energy of the quasi-bound state is magnetically tuned into degeneracy with the energy of the free atomic pair, a resonant scattering process occurs in which the s-wave scattering length diverges and both elastic and inelastic collision cross sections are dramatically enhanced. When the collision involves two distinct atoms, the underlying molecular states can possess an electric dipole moment. In this case, the application of an external electric field can couple the bound molecular states mixing their orbital character and leading to level repulsion which breaks the degeneracy for dierent orbital angular momentum projections. The result is that the electric field shifts the positions of intrinsic magnetic Feshbach resonances, generates copies of resonances previously restricted to a particular partial-wave collision to other partial-wave channels, and splits Feshbach resonances into multiple resonances for states of nonzero angular momenta. This latter phenomenon oers a way to produce and tune an anisotropic interaction in atomic mixtures and to produce p-wave molecules of particular orbital angular momenta projections (1). In this talk, we discuss recent theoretical work and experimental progress on the realization and study of these phenomena associated with electric field dressing of magnetically tunable Feshbach resonances.
The effects of combined external electric and magnetic fields on elastic collisions in ultracold Li-Rb mixtures are studied using recently obtained experimentally verified potentials. Our analysis provides both quantitative predictions for and a detailed physical interpretation of the phenomena arising from electric-field-induced interactions. It is shown that the electric field shifts the positions of intrinsic magnetic Feshbach resonances, generates copies of resonances previously restricted to a particular partial-wave collision to other partial-wave channels, and splits Feshbach resonances into multiple resonances for states of nonzero angular momenta. It was recently observed that the magnetic dipole-dipole interaction can also lift the degeneracy of a ppp-wave state splitting of the associated ppp-wave Feshbach resonance into two distinct resonances at different magnetic fields. Our work shows that the splitting of the resonances produced by an applied electric field is more than 1 order of magnitude larger. This phenomenon offers a complementary way to produce and tune an anisotropic interaction and to study its effect on the many-body physics of heteronuclear atomic gases.
We report a unique feature of magnetic-field Feshbach resonances in which atoms collide with nonzero orbital angular momentum. ppp-wave (l=1)(l=1)(l=1) Feshbach resonances are split into two components depending on the magnitude of the resonant state's projection of orbital angular momentum onto the field axis. This splitting is due to the magnetic dipole-dipole interaction between the atoms and it offers a means to tune anisotropic interactions of an ultracold gas of atoms. Furthermore this splitting in the ppp-wave Feshbach resonance has been experimentally observed and is reported. A parametrization of the ppp-wave resonance in terms of an effective-range expansion is given.
Anisotropy induced Feshbach resonances in mixture of 6Li(2S)  +  171Yb(3P2){}^{6}{\rm{Li}}{(}^{2}{\rm{S}})\;+\;{}^{171}{\rm{Yb}}{(}^{3}{{\rm{P}}}_{2})6Li(2S)+171Yb(3P2​)
We theoretically explore the scattering properties in collisions between in the ground state and fermionic in the metastable state. Unlike the role of the electronic spin degree of freedom in collisions of two alkali-metal atoms, the orbital degrees of freedom from the p electron of the metastable atoms, which induce not only mixings between different partial waves but also couplings between channels in different fine-structure manifolds, introduce the anisotropic interactions for producing broad-enough Feshbach resonances. Our closed-coupling calculation shows that this mechanism is similar to that in highly magnetic atoms, but the resonances also suffer from a large inelastic rate at the magnitude of to lower-lying fine-structure states or Zeeman sublevels, which will be an obstacle for associating ultracold polar molecules with both electron spin and electric dipole momentum. However, such a rich mixture of inelastic processes, and the experimental advantage of immunity from intraspecies inelastic collisions for metastable fermionic allow for precise investigations on the interspecies scattering properties for systems with excited-state atoms included.
This Thesis describes new mechanisms for controlling elastic and inelastic collisions of ultracold atoms and molecules with static electromagnetic and laser fields. The dynamical properties of ultracold atoms are usually tuned in experiments by applying an external magnetic field to induce a Feshbach resonance. The work presented in this Thesis demonstrates the possibility of inducing and manipulating Feshbach resonances with electric fields. We discuss in detail the mechanisms of electric-field-induced resonances in ultracold mixtures of alkali metal atoms and demonstrate that electric fields may shift and split the magnetic resonances. We show that electric fields may spin up the collision complex of ultracold atoms and induce anisotropic scattering which may be exploited in experiments on many-body dynamics of ultracold gaseous mixtures. The mechanisms of electric-field-induced resonances described in this Thesis allow for two-dimensional control of inter-particle interactions, leading to total control over ultracold gases. To guide future experiments, we generate accurate interaction potentials for ultracold Li--Rb mixtures by fitting positions and widths of experimentally measured Feshbach resonances. Ultracold atomic and molecular gases can be confined by laser fields in one or two dimensions which produces an optical lattice of ultracold particles. We develop a multichannel scattering theory for collisions of atoms and molecules in two dimensions and explore the effects of the confining laser potential on inelastic and reactive collisions of ultracold atoms and molecules in a 1D optical lattice. We show that ultracold collisions can be controlled in a quasi-2D geometry by varying the orientation of a magnetic field with respect to the confinement plane normal and demonstrate that the threshold energy dependence of cross sections for inelastic collisions in an optical lattice can be tuned by varying the confining potential and the magnetic field. Our results show that applying laser confinement in one dimension may stabilize ultracold systems with large scattering lengths, which may open up interesting opportunities for studies of ultracold controlled chemistry and might lead to a new research direction of ultracold chemistry in restricted geometries.
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. We focus on dysprosium and erbium as important experimental advances have been recently made to cool and create quantum-degenerate gases for these atoms. Finally, we describe progress in locating resonances in collisions of meta-stable magnetic atoms in electronic P-states with ground-state atoms, where an interplay between collisional anisotropies and spin-orbit coupling exists.
Ultracold molecules provide opportunities for exploring quantum matter, chemical dynamics and information processing thanks to their rich interactions, which can be controlled by external fields. Magnetic fields tune interactions through Feshbach resonances, enabling the formation of ultracold dimers and triatomic molecules from atom-dimer collisions. Here we demonstrate electric-field control of atom-molecule Feshbach resonances. In mixtures of ground-state sodium-potassium molecules and potassium atoms, electric fields shift resonance positions systematically, revealing specific trimer bound states and their electric-field dependent energies. The response differs markedly from isolated dimers, showing hindered rotation of the molecular constituent near an atom. Electric fields therefore add an independent knob for atom-molecule resonances, open spectroscopic access to triatomic quantum states, and advance controlled polyatomic quantum matter.