Controlling Magnetic Feshbach Resonances in Polar Open-Shell Molecules with Nonresonant Light

Abstract

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 non-resonant field intensities of the order of 10 9 W/cm 2 , we find the width to be increased by three orders of magnitude, reaching a few Gauss. This opens the way for producing ultracold molecules with sizeable electric and magnetic dipole moments and thus for many-body quantum simulations with such particles.PACS numbers: 34.50. Cx,34.50.Rk, Ultracold polar molecules are predicted to probe fundamental physics [1] and realize a wealth of many-body phenomena such as exotic quantum phases [2]. They are thus attracting significant interest in both the AMO and condensed matter communities [3]. Polar alkali dimers have already been produced in their absolute internal ground state close to quantum degeneracy [4], opening the way toward ultracold chemistry [5,6] and quantum simulation [7]. Contrary to ground-state alkali dimers which are closed-shell, diatomics consisting of an open-shell and a closed-shell atom possess an unpaired electron, endowing the molecule with spin structure and a significant magnetic dipole moment. Since these molecules have both electric and magnetic dipoles, they are supreme candidates for creating topologically ordered states [8], investigating collective spin excitations [9] and realizing lattice-spin models [7]. While numerous ultracold mixtures of open-shell alkali and closedshell Yb or Sr atoms have already been studied experimentally [10][11][12][13][14][15], magnetoassociating the atoms into molecules has remained an elusive goal.The most successful and widely used routes to producing ultracold dimers utilize magnetically tunable Feshbach resonances (FRs) [16,17] where the hyperfine interaction couples a scattering state to a bound molecular level. Somewhat unexpectedly, FRs have been predicted for diatomics with a 2 Σ ground electronic state such as RbSr and LiYb [18,19]. The resonances are caused by a modification of the alkali atom's hyperfine structure due to the presence of the other atom [18] or by creating a hyperfine coupling due to the alkali atom polarizing the nuclear spin density of fermionic Yb [19]. However, the width of these resonances does not exceed a few milli-Gauss. This renders their use in magnetoassociation very difficult, if not impossible. A different kind of FR for a closed-shell/open-shell mixture has recently been observed, with one of the atoms in an electronically excited state [20,21]. In this case, the FR is induced by the anisotropy of the interaction between S-state and P -state atoms. Due to the finite excited state lifetime, such a FR is not ideally suited for making molecules. It suggests, however, to harness an anisotropic interaction for magnetoassociation.Here we show that non-resonant light, which universally couples to the polarizability anisotropy of a molecu...

Asymptotic model for shape resonance control of diatomics by intense non-resonant light

“…This control is of a universal character, independent of the frequency of the light and the energy level structure of the molecule (as long as the frequency remains far from any molecular resonance). Interestingly, non-resonant light control should also enable magnetoassociation by creating new Feshbach resonances and by strongly enlarging their width [18]. A nonresonant field affects not only shape resonances but also bound rovibrational levels by shifting their energies and hybridizing their rotational motion [17,19].…”

Reexamination of the calculation of two-center, two-electron integrals over Slater-type orbitals. III. Case study of the beryllium dimer

“…[4] for interpretation of the observed subradiant states of Sr 2 . Electronic structure calculations can also be used to predict new schemes for the formation of ultracold diatomic molecules [5][6][7][8][9]. Apart from that, state-ofthe-art first-principles calculations are used in metrology e.g.…”

Impact of overlapping resonances on magnetoassociation of cold molecules in tight traps

“…It is important to find resonances with magnetic field width big enough for precise experimental control. Methods for engineering the resonance width with external electromagnetic fields can thus be useful, especially for closed-shell atoms which generally do not exhibit wide resonances [16].…”