



01444nas a2200169   4500008004100000245007500041210006900116260001500185490000600200520093200206100001701138700002201155700001901177700001901196700002201215856003701237       2018                        eng d00aObservation of bound state self-interaction in a nano-eV atom collider0 aObservation of bound state selfinteraction in a nanoeV atom coll  c2018/11/200 v93 a<p>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.</p>1 aThomas, Ryan1 aChilcott, Matthew1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels  uhttps://arxiv.org/abs/1807.01174