Quantum Tomography of Feshbach Resonance States

Quantum phenomena that lead to a formation of long-lived collision complexes, such as scattering resonances play a central role to the outcome of cold molecular collisions. These resonances are fundamental probes of the fine details of internuclear interactions and serve as a benchmark for current computational methods.

Here we present a joint experimental and theory study where we are able to generate and investigate the multi-channel decay of a Feshbach resonance state with quantum state-to-state resolution. Our method is based on the coincidence detection of electron/ion momenta in Penning ionization collisions between metastable noble gas atoms and neutral molecules. At the ionization step of the dynamics, the molecular ion-neutral atom system is generated in a specific Feshbach resonance state which is identified by the kinetic energy of the ejected electron. The kinetic energy of the product ions provides information about the decay of each resonance state to a manifold of states which differ by the final vibrational state of the molecular ion. Here, in a single measurement, we obtain both the energy and the composition at the continuum of each resonance state. Such a tomography of the Feshbach resonance states provides several tens of quantum numbers per measurement.

The experimental results pose a formidable challenge to current computational methods. We show that Feshbach state tomography allows us to probe both the short range interactions that are responsible for rovibrational and reactive dynamics as well as the long range part of the potential affecting the energy location of resonances states.

We also present an experimental scheme for control of tomography of the Feshbach states which is based on the initial constraint of total angular momentum at the Ionization step of the dynamics. The latter is motivated by our recent observation of a partial wave resonance at the lowest state of relative angular momentum.