Fano interference in quantum resonances from angle-resolved elastic scattering

Abstract

Interference of a discrete quantum state with a continuum of states gives rise to
asymmetric line shapes that have been observed in measurements across nuclear, 
atomic, molecular as well as solid-state physics. Information about the 
interference is captured by some but not all measurable quantities. For example, 
for quantum resonances arising in single channel scattering, the signature of 
such interference may disappear due to the orthogonality of partial waves. Here, 
we show that probing the angular dependence of the cross section allows for 
unveiling the coherence between the partial waves which leads to the appearance 
of the characteristic asymmetric Fano profiles. We observe a shift of the 
resonance position with observation angle, in excellent agreement with 
theoretical predictions from full quantum scattering calculations. Using a model 
description for the interference between the resonant and background states, we 
extract the relative phase responsible for the characteristic Fano-like profile 
from our experimental measurements.