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arXiv:2412.00743 · Physical Review A

Field-induced quantum interference of inelastic scattering in ultracold atomic collisions

Ting Xie, Chuan‐Cun Shu

Published Aug 1, 2025• 0 citations
arXivHTMLPDF

Abstract

Exploiting quantum interference presents a significant challenge in ultracold inelastic scattering. In this study we propose a method to verify quantum interference within the two-body loss rate that arises from multiple inelastic-scattering channels, where the colliding particles are initially prepared in their individual hyperfine states. Our approach employs a ring-coupling configuration, accomplished by combining external radio-frequency and static electric fields during ultracold atomic collisions. To validate our proposal, we perform close-coupling calculations for $^{7}\mathrm{Li}\text{\ensuremath{-}}^{41}\mathrm{K}$ collisions at the ultracold limit. The results reveal that the interference profile, as manifested in the two-body loss rate, can be verified with optimized external field parameters. Notably, our findings indicate that the two-body loss rate coefficient exhibits a distinct pattern of constructive or destructive interference when crossing a magnetically induced $p$-wave resonance in the incoming channel. These interference patterns become increasingly pronounced as the intensities of the external fields increase. This work presents a potential approach to controlling inelastic-scattering processes in ultracold collisions.

DOI
10.1103/q274-8kkw

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Exploiting quantum interference presents a significant challenge in ultracold inelastic scattering. In this study we propose a method to verify quantum interference within the two-body loss rate that arises from multiple inelastic-scattering channels, where the colliding particles are initially prepared in their individual hyperfine states. Our approach employs a ring-coupling configuration, accomplished by combining external radio-frequency and static electric fields during ultracold atomic collisions. To validate our proposal, we perform close-coupling calculations for 7Li\ensuremath-41K^{7}\mathrm{Li}\text{\ensuremath{-}}^{41}\mathrm{K}7Li\ensuremath-41K collisions at the ultracold limit. The results reveal that the interference profile, as manifested in the two-body loss rate, can be verified with optimized external field parameters. Notably, our findings indicate that the two-body loss rate coefficient exhibits a distinct pattern of constructive or destructive interference when crossing a magnetically induced ppp-wave resonance in the incoming channel. These interference patterns become increasingly pronounced as the intensities of the external fields increase. This work presents a potential approach to controlling inelastic-scattering processes in ultracold collisions.
Abstract Ultracold atoms prepared in excited internal states can escape from the trap through inelastic collisions. A magnetic field can be used to suppress the s-wave loss rate coefficient near an s-wave Feshbach resonance. However, at the temperature of μK the p-wave loss rate coefficient becomes increasingly important as the temperature increases. The unsuppressed p-wave loss rate coefficient can far exceed the suppressed s-wave loss rate coefficient, and severely restricts the reduction of the total loss rate coefficient. We calculate the collision rate coefficients of ultracold 85Rb and 87Rb atoms prepared in excited hyperfine and Zeeman states using the coupled-channel method. We find that in R b 85 ( F 1 = 3 , m F 1 = 3 ) + R b 87 ( F 2 = 1 , m F 2 = − 1 ) and R b 85 ( F 1 = 2 , m F 1 = − 2 ) + R b 87 ( F 2 = 2 ,
We propose a general method to induce interference between scattering wave functions in atomic and molecular collisions at ultracold temperatures by using a static magnetic field. The scheme is based on the preparation of collision partners in coherent superpositions of Zeeman states. The magnetic field is used to induce interference between two incoming channels. As an illustrative example, we consider ultracold collisions between 7Li^{7}\mathrm{Li}7Li and 133Cs^{133}\mathrm{Cs}133Cs atoms, and show that ratios of state resolved collision cross sections can be enhanced by engineering the preparation of the initial coherent superpositions.
This thesis has investigated the dynamics of ultracold atomic collisions in the presence of both static magnetic and oscillating radio-frequency (rf) fields. The bound state structure and scattering length of 39K+133Cs was examined in the presence of only a static magnetic field, where it was found that no Feshbach resonance of suitable width for magnetoassociation existed at a magnetic field where caesium can be cooled to degeneracy. We then showed that zero-energy Feshbach resonances may be engineered using an rf field in places where they did not previously exist. An rf field with frequency 79.9 MHz was chosen to induce a resonance near 21 G. The widths of such rf-induced Feshbach resonances increase quadratically with rf field strength. The resonances presented are lossless with circularly polarized rf, and the molecules created are long-lived even with plane-polarized RF. Collisional losses in rf-dressed magnetic traps were also investigated. An rf-induced loss mechanism that does not exist in the absence of rf radiation was identified. This mechanism is not suppressed by a centrifugal barrier in the outgoing channel, and can be much faster than spin relaxation, which is centrifugally suppressed. We explore the dependence of the rf-induced loss rate on singlet and triplet scattering lengths, hyperfine splittings and the strength of the rf field. The results were interpreted in terms of an adiabatic model of the collision dynamics, and calculate the corresponding nonadiabatic couplings. The loss rate can vary by 10 orders of magnitude as a function of singlet and triplet scattering lengths. 87Rb is a special case, where several factors combine to reduce rf-induced losses; as a result, they are slow compared to spin-relaxation losses. For most other alkali-metal pairs, rf-induced losses are expected to be much faster and may dominate. For heteronuclear mixtures an rf-modified spin-exchange mechanism was identified that results in loss rates orders of magnitude greater than the rf-induced loss rates in homonuclear cases. Fast loss is expected in mixtures where the Lande g-factors differ.
We investigate the control of two-body inelastic spin-exchange loss in ultracold atoms by applying an electric field to modulate magnetic Feshbach resonances. While conventional magnetic tuning can enhance or suppress two-body spin-exchange losses, the incorporation of an electric field introduces an additional degree of freedom, enabling more flexible control over resonances for different partial waves. Taking the 6Li-40K{}^{6}{\text{Li-}}^{40}\text{K}6Li-40K collision as an example, we demonstrate how this approach can be employed to control sss- and ppp-wave inelastic loss processes and improve the suppression of the loss rate coefficient. This study may open a new possibility for the control of ultracold atomic inelastic collisions.
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.
We calculate the rates of inelastic collisions for ultracold alkali-metal atoms in radio-frequency-dressed traps, using coupled-channel scattering calculations on accurate potential energy surfaces. We identify a radio-frequency-induced loss mechanism that does not exist in the absence of radio frequency (rf) radiation. This mechanism is not suppressed by a centrifugal barrier in the outgoing channel, and can be much faster than spin relaxation, which is centrifugally suppressed. We explore the dependence of the rf-induced loss rate on singlet and triplet scattering lengths, hyperfine splittings, and the strength of the rf field. We interpret the results in terms of an adiabatic model of the collision dynamics, and calculate the corresponding nonadiabatic couplings. The loss rate can vary by 10 orders of magnitude as a function of singlet and triplet scattering lengths. 87Rb^{87}\mathrm{Rb}87Rb is a special case, where several factors combine to reduce rf-induced losses; as a result, they are slow compared to spin-relaxation losses. For most other alkali-metal pairs, rf-induced losses are expected to be much faster and may dominate.