Fano interference in quantum resonances from angle-resolved elastic scattering

TL;DR

This paper demonstrates that angular-resolved measurements can reveal Fano interference effects in single-channel quantum resonances, which are typically hidden, by analyzing the phase and shape of elastic scattering profiles.

Contribution

It introduces a method to detect and analyze Fano interference in single-channel resonances through angular dependence, supported by experimental and theoretical quantum scattering data.

Findings

Angular dependence reveals Fano profiles in single-channel resonances.

Experimental peak shifts match quantum scattering predictions.

Partial wave analysis disentangles resonance and background contributions.

Abstract

Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states. Such line shapes are well known for multichannel systems, for example, in photoionization or Feshbach resonances in molecular scattering. On the other hand, in resonant 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 us to unveil asymmetric Fano profiles also in a single channel shape resonance. We observe a shift in the peak of the resonance profile in the elastic collisions between metastable helium and deuterium molecules with detection angle, in excellent agreement with theoretical predictions from full quantum scattering calculations. Using a model description for the partial wave interference, we can disentangle the resonant and background contributions and extract the relative phase responsible for the characteristic Fano-like profiles from our experimental measurements.