Observing Spatial Charge and Spin Correlations in a Strongly Interacting Fermi Gas

Area of Science:

• Quantum physics
• Condensed matter physics
• Ultracold atomic gases

Background:

• Two-dimensional attractive Fermi gases exhibit complex quantum phenomena.
• Understanding fermion pairing and correlations is key to characterizing superfluids.
• Mean-field theories like BCS theory provide a baseline but may miss crucial microscopic details.

Purpose of the Study:

• To microscopically probe spatial charge and spin correlations in 2D attractive Fermi gases.
• To observe fermion pairing and study correlation functions as interspin attraction varies.
• To compare experimental findings with theoretical predictions, including BCS theory and quantum Monte Carlo calculations.

Main Methods:

• Utilized atom-resolved continuum quantum gas microscopy for in situ measurements.
• Measured two- and three-point correlation functions.
• Employed local single-pair losses to measure Tan's contact and characterize short-range pair correlations.

Main Results:

• Directly observed fermion pairing and its evolution with increasing interspin attraction.
• Revealed nonlocal anticorrelations in the pair correlation function, contradicting BCS theory.
• Demonstrated the deficiency of BCS predictions even in weakly attractive regimes.
• Established a relation between two- and three-point correlations, emphasizing the role of pair correlations.
• Found excellent agreement between measured Tan's contact and numerical predictions.

Conclusions:

• The study provides a novel microscopic view of strongly correlated 2D Fermi gases.
• Nonlocal correlations are fundamental and not captured by mean-field BCS theory.
• Pair correlations play a dominant role in the behavior of these systems.