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.
Highlights
Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states
I.e. the interference of a discrete quantum state with a continuum of states giving rise to asymmetric line shapes, was first observed in experiments exciting rare gas atoms to Rydberg states[1] and later found in measurements across nuclear[2], atomic[1,3,4], molecular[5] as well as solid-state physics[6,7,8]. It was named after Ugo Fano who provided a theoretical understanding of the subject[9] by showing that the interference between a discrete excited state of an atom with a continuum state sharing the same energy leads to the appearance of asymmetric line shapes in the measured excitation spectra, which can be characterized by a ‘shape’ parameter[10]
While the Fano profiles were first introduced in atomic physics, the underlying interference mechanism is relevant for a wide variety of physical systems—both quantum[1,2,3,4,5,6,7,8] and classical[12,13,14]
Summary
Asymmetric spectral line shapes are a hallmark of interference of a quasi-bound state with a continuum of states. We demonstrate that interference is responsible for shifts in the peak position observed by probing an orbiting resonance in angle-resolved energy-dependent cross section measurements for cold elastic collisions between metastable helium and ground-state normal deuterium molecules.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
