Fermion pairing and correlations under a quantum gas microscope

Abstract

Understanding interacting quantum systems is a central goal of modern physics, with applications ranging from quantum chemistry to nuclear physics to the design of novel superconductors. This thesis describes the creation of exotic phases of quantum matter built from ultracold fermionic atoms trapped in an optical lattice, experimentally realizing the Fermi-Hubbard model. These fermionic atoms develop strong correlations as they tunnel and interact in the lattice potential. Using a novel bilayer quantum gas microscope, we detect these correlations by imaging arrays containing thousands of atoms, revealing the exact location and spin of each fermion.

We apply these techniques to directly reveal the formation of a Mott insulator of fermions with strong repulsion and the crossover to a gas of local pairs with strong attraction. At intermediate attraction, we observe correlated fermion pairs extending over multiple lattice sites, and these pairs interact to form a long range ordered state with charge-density-wave correlations. In a repulsive lattice gas, we detect local doublon-hole quantum fluctuations within the Mott insulator, which in turn establish long range magnetic order. Leveraging the technique of full density imaging, we implement model-independent thermometry of the strongly interacting system using the fluctuation-dissipation theorem, a fundamental relation guaranteed by statistical physics. Finally, we invent and realize a novel method to coherently manipulate and entangle fermion pairs within large two-dimensional arrays, with applications including robust quantum information storage and hybrid analog-digital quantum simulation. These experiments realize fundamental phenomena in condensed matter physics, and in addition demonstrate a robust platform for future exploration of the behavior of strongly interacting fermions.