Site-resolved Imaging of Fermionic Lithium-6 in an Optical Lattice

Abstract: We demonstrate site-resolved imaging of individual fermionic lithium-6 atoms in a 2D optical lattice. To preserve the density distribution during fluorescence imaging, we simultaneously cool the atoms with 3D Raman sideband cooling. This laser cooling technique, demonstrated here for the first time for lithium-6 atoms, also provides a pathway to rapid low-entropy filling of an optical lattice. We are able to determine the occupation of individual lattice sites with a fidelity >95%, enabling direct, local measurement of particle correlations in Fermi lattice systems. This ability will be instrumental for creating and investigating low-temperature phases of the Fermi-Hubbard model, including antiferromagnets and d-wave superfluidity.

• The paper introduces a novel imaging method that achieves over 95% fidelity for individual Lithium-6 atoms in a 2D optical lattice.
• It employs an adapted 3D Raman sideband cooling technique to maintain atoms in place, ensuring MHz-level trap frequencies and operation in the Lamb-Dicke regime.
• The technique enables local measurements of quantum correlations in the Fermi-Hubbard model, paving the way for deeper insights into strongly correlated fermionic systems.

Site-resolved Imaging of Fermionic $^6$Li in an Optical Lattice

The paper "Site-resolved Imaging of Fermionic $^6$Li in an Optical Lattice" presents a significant advancement in the study of fermionic quantum systems using ultracold atoms. The authors report the development of a technique that achieves site-resolved imaging of individual $^6$Li atoms in a two-dimensional optical lattice, offering a new method to probe quantum correlations with high fidelity. Such a capability is of particular interest for exploring strongly correlated systems like those described by the Fermi-Hubbard model.

The primary technical achievement is the implementation of a site-resolved quantum gas microscope for $^6$Li, a species that, until this work, had not been imaged on such a fine scale due to challenges associated with its light mass and the requirements of cooling techniques. To achieve high-fidelity imaging, the researchers employ a novel adaptation of 3D Raman sideband cooling, which successfully maintains atoms in their lattice sites during fluorescence imaging. This technique has not been previously applied to $^6$Li, marking an instrumental development for studies in low-entropy lattice systems.

A key result is the demonstration of imaging fidelity greater than 95%, allowing for the precise determination of lattice site occupation. This high level of precision opens new opportunities for measuring local particle correlations, making advances in the understanding of many-body phenomena such as antiferromagnetism and d-wave superfluidity within the Fermi-Hubbard model. Such measurement capabilities are critical for validating theoretical models, particularly where computational approaches are limited by challenges like the sign problem in Quantum Monte Carlo simulations.

The researchers highlight several technical details that underscore the capability of their approach. By achieving MHz-level trap frequencies, they ensure the system remains in the Lamb-Dicke regime during imaging—a prerequisite for preserving vibrational states through the cooling process. The optimized Raman imaging sequence not only allows for sufficient photon collection per atom but also ensures the fidelity of occupancy determination through a comprehensive fitting algorithm.

Practically, this development paves the way for experiments aimed at uncovering the properties of low-temperature phases of fermionic systems. The ability to perform local measurements of spin correlations and entropic properties in Fermi lattices represents a foundational tool for quantum simulation, potentially guiding the optimization of materials with novel quantum properties like high-temperature superconductors.

Theoretically, this work illustrates the growing capability of synthetic quantum systems to replicate and provide insights into complex many-body phenomena. The adaptability of ultracold atomic systems for tunability and control continues to strengthen their role as experimental platforms for condensed matter physics.

Looking forward, this method has the potential to be combined with advancements in optical potentials to achieve single-atom addressability, further enhancing the scope of quantum simulation platforms. The techniques developed here may eventually contribute to lower entropy sample preparation, improving the experimental realization of quantum phases and transitions pertinent to both fundamental physics and potential technological applications.

Overall, the results presented in this paper make significant contributions to the toolbox of experimental quantum physics, providing a framework for future explorations into the behaviors and emergent properties of interacting quantum systems.