The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and Efimov physics are two distinct quantum phenomena in condensed matter and nuclear physics, respectively. The RKKY interaction describes correlations between impurities mediated by an electron gas, while Efimov physics describes universal bound states of three particles with resonant interactions. Recently, both effects have been observed in Bose-Fermi mixtures in the weak and resonant interaction regimes, respectively. Intriguing conjectures exist to elucidate how the two phenomena meet in the transition regime where the mixture is strongly interacting. In this Letter, we explore the RKKY-Efimov transition in a mixture of bosonic ^{133}Cs and fermionic ^{6}Li near a tunable interspecies Feshbach resonance. From dispersion and relaxation measurements, we find that the transition is highlighted by a fermion-mediated scattering resonance between Cs atoms and a weaker resonance on Li atoms. These resonances represent reactive scattering of Cs and Li atoms in the many-body regime, which reduce to an Efimov resonance in the thermal gas regime. Our observation demonstrates the intriguing interplay of two-, three-, and many-body physics in a Bose-Fermi mixture that connects condensed matter physics, nuclear physics, and quantum many-body chemistry.The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and Efimov physics are two distinct quantum phenomena in condensed matter and nuclear physics, respectively. The RKKY interaction describes correlations between impurities mediated by an electron gas, while Efimov physics describes universal bound states of three particles with resonant interactions. Recently, both effects have been observed in Bose-Fermi mixtures in the weak and resonant interaction regimes, respectively. Intriguing conjectures exist to elucidate how the two phenomena meet in the transition regime where the mixture is strongly interacting. In this Letter, we explore the RKKY-Efimov transition in a mixture of bosonic ^{133}Cs and fermionic ^{6}Li near a tunable interspecies Feshbach resonance. From dispersion and relaxation measurements, we find that the transition is highlighted by a fermion-mediated scattering resonance between Cs atoms and a weaker resonance on Li atoms. These resonances represent reactive scattering of Cs and Li atoms in the many-body regime, which reduce to an Efimov resonance in the thermal gas regime. Our observation demonstrates the intriguing interplay of two-, three-, and many-body physics in a Bose-Fermi mixture that connects condensed matter physics, nuclear physics, and quantum many-body chemistry.

arXiv:2502.06266Physical Review LettersNov 13, 20250 citations

Probing quantum effects in lithium

Rong Zhang, Shanti Deemyad

Bulletin of the American Physical SocietyMar 6, 20180 citations

Heteronuclear Efimov Scenario with Positive Intraspecies Scattering Length

Juris Ulmanis, Stephan Häfner, R. Pires +4 more

We investigate theoretically and experimentally the heteronuclear Efimov scenario for a three-body system that consists of two bosons and one distinguishable particle with positive intraspecies scattering lengths. The three-body parameter at the three-body scattering threshold and the scaling factor between consecutive Efimov resonances are found to be controlled by the scattering length between the two bosons, approximately independent of short-range physics. We observe two excited-state Efimov resonances in the three-body recombination spectra of an ultracold mixture of fermionic ^{6}Li and bosonic ^{133}Cs atoms close to a Li-Cs Feshbach resonance, where the Cs-Cs interaction is positive. Deviation of the obtained scaling factor of 4.0(3) from the universal prediction of 4.9 and the absence of the ground state Efimov resonance shed new light on the interpretation of the universality and the discrete scaling behavior of heteronuclear Efimov physics.We investigate theoretically and experimentally the heteronuclear Efimov scenario for a three-body system that consists of two bosons and one distinguishable particle with positive intraspecies scattering lengths. The three-body parameter at the three-body scattering threshold and the scaling factor between consecutive Efimov resonances are found to be controlled by the scattering length between the two bosons, approximately independent of short-range physics. We observe two excited-state Efimov resonances in the three-body recombination spectra of an ultracold mixture of fermionic ^{6}Li and bosonic ^{133}Cs atoms close to a Li-Cs Feshbach resonance, where the Cs-Cs interaction is positive. Deviation of the obtained scaling factor of 4.0(3) from the universal prediction of 4.9 and the absence of the ground state Efimov resonance shed new light on the interpretation of the universality and the discrete scaling behavior of heteronuclear Efimov physics.

arXiv:1608.01477Physical Review LettersOct 7, 201657 citations

Toward Simultaneous Quantum Degeneracy of

^{133}

Cs and

^6

Li Atoms