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  • Open Access

Site-Resolved Imaging of Ultracold Fermions in a Triangular-Lattice Quantum Gas Microscope

Jin Yang†, Liyu Liu†, Jirayu Mongkolkiattichai†, and Peter Schauss*

  • Department of Physics, University of Virginia, Charlottesville, Virginia 22904, USA
  • *ps@virginia.edu
  • †These authors contributed equally to this work.
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PRX Quantum 2, 020344 – Published 21 June, 2021

DOI: https://doi.org/10.1103/PRXQuantum.2.020344

Abstract

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 6Li 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 D1 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 approximately 98%. Our 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.

Physics Subject Headings (PhySH)

Popular Summary

Ultracold atoms in optical lattices enable quantum simulation of electrons in solids in a well-controlled and widely tunable setting. In Fermi-Hubbard models, the electrons in the ionic lattice can be simulated by fermionic atoms in an optical lattice. Quantum gas microscopes allow these systems to be studied with the ultimate resolution of a single atom. For antiferromagnetic interactions, opposite spins on neighboring sites are energetically preferred. Therefore, lattice geometries can be divided into two categories, depending on the compatibility with staggered ordering. If the staggered ordering is allowed, it is the ground state. However, in a triangular lattice staggered ordering is not possible and more interesting ground states can emerge. This effect is known as geometric frustration, leading to a huge degeneracy in the ground state, and exotic quantum states such as spin liquids. A quantum simulation platform for those systems is sought-after but, up to now, it was unknown how quantum gas microscopy could be extended to fermions in triangular lattices.

Here, we demonstrate a quantum gas microscope to image individual fermionic atoms in a triangular lattice. We prepare a degenerate Fermi gas, load it into the triangular lattice, and image the individual atoms with high imaging fidelity using Raman sideband cooling. Our triangular-lattice platform will allow the study of density and spin correlations in frustrated Hubbard models to observe the strange properties of frustrated systems, including quantum spin liquids without long-range ordering at zero temperature, time-reversal symmetry breaking, and spin-hole bound states with significance to the understanding of superfluidity.

Article Text

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Outline

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PRX Quantum 2, 020344– Published 21 June, 2021
  • Received 22 February 2021
  • Accepted 20 May 2021
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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