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.

arXiv comment6 pages, 4 figures, Links to 3 pages of Supplementary Information and 1 Supplementary Movie

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• Low-cost Wireless Condition Monitoring for an Ultracold Atom Machine
• Width and shift of Fano-Feshbach resonances for van der Waals interactions
• Scattering halos in strongly interacting Feshbach molecular Bose-Einstein condensates
• Observing S-Matrix Pole Flow in Resonance Interplay: Cold Collisions of Ultracold Atoms in a Miniature Laser-based Accelerator
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