Antiflatness and nonlocal nonstabilizerness in two-particle scattering processes

Nonlocal nonstabilizerness (NL NS) and antiflatness provide a measure of the quantum complexity in the wave function of a physical system. Supported by entanglement, they cannot be removed by local unitary operations, thus providing basis-independent measures, and sufficiently large values underpin the need for quantum computers in order to perform precise simulations of the system at scale. Towards a better understanding of the quantum-complexity generation by fundamental interactions, the building blocks of many-body systems, we consider nonlocal nonstabilizerness and antiflatness in two-particle scattering processes, specifically focusing on low-energy nucleon-nucleon scattering and high-energy Møller scattering. We find that the nonlocal nonstabilizerness induced in both interactions is four times the antiflatness (which is found to be true for any two-qubit wave function), and verify the relation between the Clifford-averaged antiflatness and total nonstabilizerness. For these processes, the antiflatness is a more experimentally accessible quantity as it can be determined from one of the final-state particles, and does not require spin correlations. While the Møller experiment at the Thomas Jefferson National Accelerator Facility does not include final-state spin measurements, the results presented here may add motivation to consider their future inclusion.