The Pauli exclusion principle is the fundamental law underpinning the structure of matter. Due to their anti-symmetric wave function no two fermions can occupy the same quantum state. It has been predicted that this leads to the formation of striking geometric structures, termed Pauli Crystals, when confining fermions in some potential. In contrast to true crystalline phases, these unique high-order density correlations emerge even without any interactions present. Here, we report the direct observation of Pauli Crystals in a system of ultracold atoms, confined to a two-dimensional harmonic oscillator potential. The measurement relies on a single-atom sensitive imaging scheme in momentum space. Our work lays the foundation for future studies of correlations in strongly interacting systems of many fermions.

M. Holten, L. Bayha, K. Subramanian, C. Heintze, P. M. Preiss and S. Jochim, “Observation of Pauli Crystals”, Phys. Rev. Lett. 126, 020401 (2021)


Related to Project: C01, C02