Fano interference in quantum resonances from angle-resolved elastic scattering

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

Determining the nature of quantum resonances by probing elastic and reactive scattering in cold collisions

Scattering resonances play a central role in collision processes in physics and chemistry. They help build an intuitive understanding of the collision dynamics due to the spatial localization of the scattering wavefunctions. For resonances that are localized in the reaction region, located at short separation behind the centrifugal barrier, sharp peaks in the reaction rates are the characteristic signature, observed recently with state-of-the-art experiments in low-energy collisions. If, however, the localization occurs outside of the reaction region, mostly the elastic scattering is modified. This may occur due to above-barrier resonances, the quantum analogue of classical orbiting. By probing both elastic and inelastic scattering of metastable helium with deuterium molecules in merged-beam experiments, we differentiate between the nature of quantum resonances—tunnelling resonances versus above-barrier resonances—and corroborate our findings by calculating the corresponding scattering wavefunctions

Phase protection of Fano-Feshbach resonances

Decay of bound states due to coupling with free particle states is a general phenomenon occurring at energy scales from MeV in nuclear physics to peV in ultracold atomic gases. Such a coupling gives rise to Fano-Feshbach resonances (FFR) that have become key to understanding and controlling interactions—in ultracold atomic gases, but also between quasiparticles, such as microcavity polaritons. Their energy positions were shown to follow quantum chaotic statistics. In contrast, their lifetimes have so far escaped a similarly comprehensive understanding. Here, we show that bound states, despite being resonantly coupled to a scattering state, become protected from decay whenever the relative phase is a multiple of π. We observe this phenomenon by measuring lifetimes spanning four orders of magnitude for FFR of spin–orbit excited molecular ions with merged beam and electrostatic trap experiments. Our results provide a blueprint for identifying naturally long-lived states in a decaying quantum system

Paracentral Acute Middle Maculopathy: A Case Report

Paracentral Acute Middle Maculopathy (PAMM) is an optical coherence tomography finding observed in patients with retinal capillary ischaemia. It is a type of ischaemic maculopathy that affects the intermediate and deep retinal capillary plexuses. PAMM has been associated with various retinal vascular disorders such as retinal artery and venous occlusions, diabetic retinopathy, sickle cell anaemia, and Purtscher retinopathy. It can also occur following a flu-like illness and transorbital compression. The authors present a case of a 37-year-old healthy female patient who exhibited signs and symptoms suggestive of PAMM a few days after experiencing a self-limiting flu-like illness

Observation of the p-wave shape resonance in atom-molecule collisions

We observe a p-wave resonance in the collisions between metastable neon and rovibrationally ground state HD molecules at a collision energy of k_{B}×22 mK. This is the first observation of the lowest quasibound angular momentum state in molecular collisions. This measurement was enabled by the reduction of the lowest collision energy achieved without laser cooling, using the phase-space correlation in cold molecular beams. We demonstrate that contrary to higher l-state resonances, the p-wave resonance allows sensitive probing of the leading term of the van der Waals intermolecular interaction. Furthermore, the same sensitivity to the long range part of the interaction potential allows an accurate estimation of p-wave resonance lifetime using only fundamental constants and the dispersion coefficient