  Quantum gas microscopes have expanded the capabilities of quantum simulation
of Hubbard models by enabling the study of spatial spin and density
correlations in square lattices. However, quantum gas microscopes have not been
realized for fermionic atoms in frustrated geometries. Here, we demonstrate the
single-atom resolved imaging of ultracold fermionic $^{6}$Li atoms in a
triangular optical lattice with a lattice constant of 1003 nm. The optical
lattice is formed by a recycled narrow-linewidth, high-power laser combined
with a light sheet to allow for Raman sideband cooling on the $D_1$ line. We
optically resolve single atoms on individual lattice sites using a
high-resolution objective to collect scattered photons while cooling them close
to the two-dimensional ground vibrational level in each lattice site. By
reconstructing the lattice occupation, we measure an imaging fidelity of ~98%.
Our new triangular lattice microscope platform for fermions clears the path for
studying spin-spin correlations, entanglement and dynamics of geometrically
frustrated Hubbard systems which are expected to exhibit exotic emergent
phenomena including spin liquids and kinetic frustration.
