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arXiv:1612.02555 · Physical Review A

Charge transfer in ultracold gases via Feshbach resonances

Marko Gacesa, Robin Côté

Published Jun 15, 2017• 9 citations
arXivHTMLPDF

Abstract

We investigate the prospects of using magnetic Feshbach resonance to control charge exchange in ultracold collisions of heteroisotopic combinations of atoms and ions of the same element. The proposed treatment, readily applicable to alkali or alkaline-earth metals, is illustrated on cold collisions of $^{9}\mathrm{Be}^{+}$ and $^{10}\mathrm{Be}$. Feshbach resonances are characterized by quantum scattering calculations in a coupled-channel formalism that includes non-Born-Oppenheimer terms originating from the nuclear kinetic operator. Near a resonance predicted at 322 G, we find the charge exchange rate coefficient to rise from practically zero to values greater than ${10}^{\ensuremath{-}12}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}$/s. Our results suggest controllable charge exchange processes between different isotopes of suitable atom-ion pairs, with potential applications to quantum systems engineered to study charge diffusion in trapped cold atom-ion mixtures and emulate many-body physics.

DOI
10.1103/physreva.95.062704

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We investigate the prospects of using magnetic Feshbach resonance to control charge exchange in ultracold collisions of heteroisotopic combinations of atoms and ions of the same element. The proposed treatment, readily applicable to alkali or alkaline-earth metals, is illustrated on cold collisions of 9Be+^{9}\mathrm{Be}^{+}9Be+ and 10Be^{10}\mathrm{Be}10Be. Feshbach resonances are characterized by quantum scattering calculations in a coupled-channel formalism that includes non-Born-Oppenheimer terms originating from the nuclear kinetic operator. Near a resonance predicted at 322 G, we find the charge exchange rate coefficient to rise from practically zero to values greater than 10\ensuremath−12cm3{10}^{\ensuremath{-}12}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{3}10\ensuremath−12cm3/s. Our results suggest controllable charge exchange processes between different isotopes of suitable atom-ion pairs, with potential applications to quantum systems engineered to study charge diffusion in trapped cold atom-ion mixtures and emulate many-body physics.
We investigate magnetically tunable Feshbach resonances between ultracold europium atoms and between europium and alkali-metal atoms using multichannel quantum scattering calculations. For ultracold gases of europium atoms both homonuclear 153Eu+153Eu^{153}\mathrm{Eu}+^{153}\mathrm{Eu}153Eu+153Eu and heteronuclear 151Eu+153Eu^{151}\mathrm{Eu}+^{153}\mathrm{Eu}151Eu+153Eu systems are studied. Calculations for mixtures of europium and alkali-metal atoms are carried out for prototype systems of 153Eu+87Rb^{153}\mathrm{Eu}+^{87}\mathrm{Rb}153Eu+87Rb and 153Eu+7Li^{153}\mathrm{Eu}+^{7}\mathrm{Li}153Eu+7Li. We analyze the prospects for the control of scattering properties, observation of quantum chaotic behavior, and magnetoassociation into ultracold polar and paramagnetic molecules. We show that favorable resonances can be expected at experimentally feasible magnetic-field strengths below 1000G1000\phantom{\rule{0.28em}{0ex}}\mathrm{G}1000G for all investigated atomic combinations. For Eu atoms, a rich spectrum of resonances is expected as a result of the competition between relatively weak short-range spin-exchange and strong long-range magnetic dipole-dipole interactions, where the dipolar interaction induces measurable resonances. A high density of resonances is expected at magnetic-field strengths below 200G200\phantom{\rule{0.28em}{0ex}}\mathrm{G}200G without pronounced quantum chaos signatures. The present results may be useful for the realization and application of dipolar atomic and molecular quantum gases based on europium atoms in many-body physics.
This thesis presents the investigation of the two-body scattering properties of cold atoms in \nsodium and lithium-sodium mixtures and their effects on the many body dynamics. Since both \nspecies are alkali atoms, the combined spin of both unpaired electrons can be either zero or one, \nproviding two different scattering channels. \nThe coupling of bound molecular states in these channels with the free atoms asymptote \ngives rise to the rich field of Feshbach resonance physics, where the interaction between the \nparticles can be controlled as an easily accessible experimental parameter. We have investigated \nthe Feshbach spectrum in the bosonic 7LiNa mixture and could confirm predictions based on \n6LiNa measurements, with a shift of the predicted spectrum by about 50 G. Also, the prospects \nof interaction tuning via Feshbach resonances were examined. \nThe difference of the scattering lengths of the electronic potentials also causes a coupling \nof atomic collisional channels, which can enable a spin exchange between the atoms. In this \nthesis, spin exchange processes have been studied in coherent oscillations in a thermal gas and \na Bose-Einstein condensate of sodium, as well as the evolution of this spinor gas into its ground \nstate. Preliminary studies of the heteronuclear spin exchange process in both the bosonic 7LiNa \nand in the fermionic-bosonic mixture 6LiNa are presented as well.
We explore collisions of atomic particles in two different regimes. In the first part of this work, we study atom-atom collisions of alkali metals at ultracold temperatures and conditions typically found in modern experiments. Feshbach resonances induced by external magnetic fields present a way to change collisional properties and exhibit control over cold collisions. We perform a fully quantum coupled-channel calculation in molecular orbital formalism to calculate collisional properties and characterize Feshbach resonances in ultracold Li+Na and Li+Rb systems. Furthermore, we use the results of these calculations as a foundation to propose a novel scheme for formation of stable ultracold molecules in their lowest rovibrational level. The formation scheme relies on the fact that the photoassociation rate becomes greatly enhanced in the vicinity of a Feshbach resonance, resulting in a large increase of the number of produced excited molecules. Efficient production of stable ultracold molecules is a prerequisite for realization of various proposed platforms for quantum computing with neutral atoms and molecules. In addition, we suggest a way to exploit specifics of the photoassociation rate behavior near its minimum for a precision measurement experiment to detect hypothetical variation of the electron-proton mass ratio in time. ^ The second part of this study examines ion-atom collisions in our solar system. Highly charged ions present in the solar wind collide with neutrals, capture one or more electrons into high excited states and deexcite, radiating energetic X-ray and UV photons. In particular, we study X-ray emissions charge-exchange collisions between fully stripped C6+, N7+ and O8+ solar wind ions and heliospheric hydrogen. We analytically solve the two-center Schrödinger equation and construct electronic potential curves for the aforementioned molecular ions. Subsequently, we compute polarization of the X-rays emitted in a single-step deexcitation following charge-exchange collisions and construct a polarization map for the ecliptic plane, as observed from Earth. Our analysis indicates that the heliospheric charge-exchange X-rays are slightly polarized, with the polarization P close to ten percent for the optimal line-of-sight. ^
We study atom-ion scattering in the ultracold regime. To this aim, an analytical model based on the multichannel quantum-defect formalism is developed and compared to close-coupled numerical calculations. We investigate the occurrence of magnetic Feshbach resonances, focusing on the specific 40Ca++Na^{40}\mathrm{Ca}^{+}+\mathrm{Na}40Ca++Na system. The presence of several resonances at experimentally accessible magnetic fields should allow the atom-ion interaction to be precisely tuned. A fully quantum-mechanical study of charge-exchange processes shows that charge-exchange rates should remain small even in the presence of resonance effects. Most of our results can be cast in a system-independent form and are important for the realization of charge-neutral ultracold systems.
Magnetically tunable Feshbach resonances exist in ultracold collisions between atoms in 2S^{2}\mathrm{S}2S and 3P0{}^{3}{\mathrm{P}}_{0}3P0​ states, such as an alkali-metal atom colliding with Yb or Sr in a clock state. We investigate the mechanisms of these resonances and identify the terms in the collision Hamiltonian responsible for them. They involve indirect coupling between the open and closed channels, via intermediate channels involving atoms in 3P1{}^{3}{\mathrm{P}}_{1}3P1​ states. The resonance widths are generally proportional to the square of the magnetic field and are strongly enhanced when the magnitude of the background scattering length is large. For any given pair of atoms, the scattering length can be tuned discretely by choosing different isotopes of the 3P0{}^{3}{\mathrm{P}}_{0}3P0​ atom. For each combination of an alkali-metal atom and either Yb or Sr, we consider the prospects of finding an isotopic combination that has both a large background scattering length and resonances at a high but experimentally accessible field. We conclude that 87Rb+Yb^{87}\mathrm{Rb}+\mathrm{Yb}87Rb+Yb, Cs+Yb\mathrm{Cs}+\mathrm{Yb}Cs+Yb, and 85Rb+Sr^{85}\mathrm{Rb}+\mathrm{Sr}85Rb+Sr are particularly promising combinations.