Observing S-Matrix Pole Flow in Resonance Interplay: Cold Collisions of Ultracold Atoms in a Miniature Laser-based Accelerator

TL;DR

This paper explores resonance phenomena in ultracold atom collisions using a laser-based accelerator, revealing the dynamics of S-matrix poles and their interplay, with implications for creating bound states in the continuum.

Contribution

It demonstrates experimental observation of S-matrix pole flow in ultracold collisions and explores resonance interplay using magnetic Feshbach resonances.

Findings

Observation of Feshbach and shape resonances in ultracold collisions

Experimental mapping of S-matrix pole flow in parameter space

Discussion of potential for bound-state-in-the-continuum creation

Abstract

We provide an overview of experiments exploring resonances in the collision of ultracold clouds of atoms. Using a laser-based accelerator that capitalizes on the energy resolution provided by the ultracold atomic setting, we unveil resonance phenomena such as Feshbach and shape resonances in their quintessential form by literally photographing the halo of outgoing scattered atoms. We exploit the tunability of magnetic Feshbach resonances to instigate an interplay between scattering resonances. By experimentally recording the scattering in a parameter space spanned by collision energy and magnetic field, we capture the imprint of the $S$-matrix pole flow in the complex energy plane. After revisiting experiments that place a Feshbach resonance in the proximity of a shape resonance and an anti-bound state, respectively, we discuss the possibility of using $S$-matrix pole interplay between two Feshbach resonances to create a bound-state-in-the-continuum.