We theoretically study the static and dynamic behavior of a BEC immersed in a large Fermi sea of ultracold atoms under conditions of tunable interspecies interaction. The degenerate Bose-Fermi mixture is kept in an elongated trap, typical for a single-beam optical dipole trap. We focus on the case of repulsive Bose-Fermi interaction and develop mean-field models to simulate the system over a wide range of repulsion strength. We further get analytical solutions in the regimes of phase separation and weak interaction. We obtain static density profiles and the frequency of the radial breathing mode, which is an elementary dynamic phenomenon of the mixture. Our results unveil the structure of the Bose-Fermi interface and describe the origin of the frequency shift of the breathing mode when the components become phase-separated at strong repulsion. We show that the mediated interaction between bosons induced by the Fermi sea can be understood as an adiabatic second-order mean-field effect, which is valid also beyond the weak-interaction regime for relevant experimental conditions. These results are consistent with our recent observations [Lous et al., Phys. Rev. Lett. 120, 243403 (2018); Huang et al., Phys. Rev. A 99, 041602(R) (2019)] in a mixture of $^{41}\mathrm{K}$ and $^{6}\mathrm{Li}$ .We theoretically study the static and dynamic behavior of a BEC immersed in a large Fermi sea of ultracold atoms under conditions of tunable interspecies interaction. The degenerate Bose-Fermi mixture is kept in an elongated trap, typical for a single-beam optical dipole trap. We focus on the case of repulsive Bose-Fermi interaction and develop mean-field models to simulate the system over a wide range of repulsion strength. We further get analytical solutions in the regimes of phase separation and weak interaction. We obtain static density profiles and the frequency of the radial breathing mode, which is an elementary dynamic phenomenon of the mixture. Our results unveil the structure of the Bose-Fermi interface and describe the origin of the frequency shift of the breathing mode when the components become phase-separated at strong repulsion. We show that the mediated interaction between bosons induced by the Fermi sea can be understood as an adiabatic second-order mean-field effect, which is valid also beyond the weak-interaction regime for relevant experimental conditions. These results are consistent with our recent observations [Lous et al., Phys. Rev. Lett. 120, 243403 (2018); Huang et al., Phys. Rev. A 99, 041602(R) (2019)] in a mixture of $^{41}\mathrm{K}$ and $^{6}\mathrm{Li}$.

arXiv:2004.09227Physical Review AJun 15, 20205 citations

Quasipure Bose-Einstein Condensate Immersed in a Fermi Sea

Florian Schreck, Lev Khaykovich, Kristan L. Corwin +4 more

We report the observation of coexisting Bose-Einstein condensate (BEC) and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the ${}^{7}\mathrm{Li}$ condensate is quasipure and in thermal contact with a ${}^{6}\mathrm{Li}$ Fermi gas. The lowest common temperature is $0.28\ensuremath{\mu}\mathrm{K}\ensuremath{\simeq}0.2(1){T}_{\mathrm{C}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2(1){T}_{\mathrm{F}}$ where ${T}_{\mathrm{C}}$ is the BEC critical temperature and ${T}_{\mathrm{F}}$ the Fermi temperature. The ${}^{7}\mathrm{Li}$ condensate has a one-dimensional character.We report the observation of coexisting Bose-Einstein condensate (BEC) and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the ${}^{7}\mathrm{Li}$ condensate is quasipure and in thermal contact with a ${}^{6}\mathrm{Li}$ Fermi gas. The lowest common temperature is $0.28\ensuremath{\mu}\mathrm{K}\ensuremath{\simeq}0.2(1){T}_{\mathrm{C}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2(1){T}_{\mathrm{F}}$ where ${T}_{\mathrm{C}}$ is the BEC critical temperature and ${T}_{\mathrm{F}}$ the Fermi temperature. The ${}^{7}\mathrm{Li}$ condensate has a one-dimensional character.

arXiv:cond-mat/0107442Physical Review LettersAug 7, 2001866 citations

Collective excitations of a quasi two-dimensional BEC: beyond mean field theory

Anoop Pappali Dilip, R. B. Thayyullathil

The European Physical Journal DMar 1, 20132 citations

^{41}\mathrm{K}

and

^{6}\mathrm{Li}

We report the observation of coexisting Bose-Einstein condensate (BEC) and Fermi gas in a magnetic trap. With a very small fraction of thermal atoms, the

{}^{7}\mathrm{Li}

condensate is quasipure and in thermal contact with a

{}^{6}\mathrm{Li}

Fermi gas. The lowest common temperature is $0.28\ensuremath{\mu}\mathrm{K}\ensuremath{\simeq}0.2(1){T}_{\mathrm{C}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2(1){T}_{\mathrm{F}}$ where

{T}_{\mathrm{C}}

is the BEC critical temperature and

{T}_{\mathrm{F}}

the Fermi temperature. The

{}^{7}\mathrm{Li}

condensate has a one-dimensional character.