Observation of bound state self-interaction in a nano-eV atom collider

Abstract

Quantum mechanical scattering resonances for colliding particles occur when a continuum scattering state couples to a discrete bound state between them. The coupling also causes the bound state to interact with itself via the continuum and leads to a shift in the bound state energy, but, lacking knowledge of the bare bound state energy, measuring this self-energy via the resonance position has remained elusive. Here, we report on the direct observation of self-interaction by using a nano-eV atom collider to track the position of a magnetically-tunable Feshbach resonance through a parameter space spanned by energy and magnetic field. Our system of potassium and rubidium atoms displays a strongly non-monotonic resonance trajectory with an exceptionally large self-interaction energy arising from an interplay between the Feshbach bound state and a different, virtual bound state at a fixed energy near threshold.

Width and shift of Fano-Feshbach resonances for van der Waals interactions

“…This insight will be crucial for the construction of effective interactions that can be used to treat few-or many-body problems, while faithfully reproducing the physics of Fano-Feshbach resonances. Experimentally, the determination of the shift is possible, as demonstrated recently [28]. The proposal in Ref.…”

“…Then, using the zero-energy analytical solutions (27)(28) of the van der Waals problem (which are also valid at low energy for R k −1 ), one finds for small k,…”

Microscopy of an ultranarrow Feshbach resonance using a laser-based atom collider: A quantum defect theory analysis

“…The deviation from linear is the manifestation of the interaction between states. Indeed, examples of such behaviour has previously been found for a Feshbach resonance interacting with an antibound state [27,61], and a p-wave shape resonance [62].…”

Effects of quantum mechanical identity in particle scattering: experimental observations (and lack thereof)

“…Over the past decade a laser-based collider for ultracold atoms has been constructed at the University of Otago (Rakonjac et al 2012;Thomas et al 2016;Horvath et al 2017;Thomas et al 2018;. This optical collider makes use of the fact that, generally, polarisable neutral particles can be confined and manipulated by laser light (Ashkin 1997).…”