Quantum-logic detection of collisions between single atom-ion pairs

Studies of interactions between a single pair of atoms in a quantum state are a corner stone of quantum chemistry. Yet, the number of demonstrated techniques that enable observation and control of the outcome of a single collision is still small. Hybrid atom-ion systems provide exquisite control over the physical state of both particles and allow to observe collisions of a single ultracold ion-atom pair. However, the necessary degree of control in the particles preparation and detection often severely limits the range of investigated atomic and molecular species. In this work, we report on a new technique to probe the inelastic reactions between a single ion and a single atom using the tools of quantum logic. A spectator logic ion, which is fully experimentally controlled, enables to probe a single chemical reaction that occurred on a co-trapped ion, on which we have a limited control. We demonstrate this method by measuring the exothermic hyperfine spin-exchange rate of an ultracold rubidium atom and four different isotopes of strontium ion. The reaction is detected in a single-shot with high efficiency. We show that by tuning this method, it can be used for detecting elastic and endothermic reactions. The presented technique can be implemented for detection of reaction cross-sections, quantum resonances and reaction dynamics of atomic and molecular species that have a limited accessibility.