Strongly Interacting Bose-Fermi Mixtures: Mediated Interaction, Phase Diagram, and Sound Propagation

Area of Science:

• Quantum physics
• Ultracold atomic gases
• Bose-Fermi mixtures

Background:

• Recent experiments show surprising behavior in Bose-Fermi mixtures.
• Existing perturbation theories struggle with strong interspecies interactions near resonance.

Purpose of the Study:

• Develop a robust strong-coupling theory for Bose-Fermi mixtures.
• Accurately model resonant interspecies interactions and satisfy the compressibility sum rule.
• Explain experimental observations and predict new phenomena.

Main Methods:

• Developed a novel strong-coupling theory for Bose-Fermi mixtures.
• Incorporated resonant interspecies interactions and the compressibility sum rule.
• Generalized fermion-mediated interactions to strong scattering and finite frequencies.

Main Results:

• The theory predicts Bose-Fermi mixtures are stable at large interaction strengths near resonance, contradicting perturbation theory.
• Calculated sound velocity for the ^{133}Cs-^{6}Li mixture, showing agreement with experiments across interaction strengths.
• Predicted hybridization of Bose and Fermi sound modes.

Conclusions:

• The developed strong-coupling theory provides a reliable framework for Bose-Fermi mixtures with strong interactions.
• The theory successfully explains experimental findings and offers new predictions for sound mode hybridization.
• This work opens avenues for further experimental and theoretical investigations of quantum gases.