Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1812.06445 · Physical Review A

Breathing mode of a Bose-Einstein condensate repulsively interacting with a fermionic reservoir

Bo Huang, Isabella Fritsche, Rianne S. Lous, Cosetta Baroni, Jook T. M. Walraven, Emil Kirilov, Rudolf Grimm

Published Apr 3, 2019• 31 citations
arXivHTMLPDF

Abstract

We investigate the fundamental breathing mode of a small-sized elongated Bose-Einstein condensate coupled to a large Fermi sea, which consists of fully spin-polarized atoms in the collisionless regime. Our observations show a dramatic shift of the breathing frequency when the mixture undergoes phase separation at strong interspecies repulsion. We find that the maximum frequency shift in the full phase-separation limit depends essentially on the atom number ratio of the components. We interpret the experimental observations by modeling the complex dynamics of the collisionless fermions within two complementary approaches. One model assumes an adiabatic response of the Fermi sea, while the other one considers single fermion trajectories for a fully phase-separated mixture. Our models capture the observed features over the full range of interest.

DOI
10.1103/physreva.99.041602

Related papers

Breathing Mode of a Bose-Einstein Condensate Immersed in a Fermi Sea

Piotr T. Grochowski, Tomasz Karpiuk, Mirosław Brewczyk +1 more

By analyzing the breathing mode of a Bose-Einstein condensate repulsively interacting with a polarized fermionic cloud, we further the understanding of a Bose-Fermi mixture recently realized by Lous et al. [Phys. Rev. Lett. 120, 243403 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.243403]. We show that a hydrodynamic description of a domain wall between bosonic and fermionic atoms reproduces the experimental data of Huang et al. [Phys. Rev. A 99, 041602(R) (2019)PLRAAN2469-992610.1103/PhysRevA.99.041602]. Two different types of interaction renormalization are explored, based on lowest-order constrained variational and perturbation techniques. In order to replicate nonmonotonic behavior of the oscillation frequency observed in the experiment, temperature effects have to be included. We find that the frequency down-shift is caused by the fermion-induced compression and rethermalization of the bosonic species as the system is quenched into the strongly interacting regime.

arXiv:1911.10582•Physical Review Letters•Sep 2, 2020•15 citations

Bose-Einstein condensate immersed in a Fermi sea: Theory of static and dynamic behavior across phase separation

Bo Huang

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:2004.09227•Physical Review A•Jun 15, 2020•5 citations

Probing the Interface of a Phase-Separated State in a Repulsive Bose-Fermi Mixture

Rianne S. Lous, Isabella Fritsche, Michael Jag +4 more

We probe the interface between a phase-separated Bose-Fermi mixture consisting of a small Bose-Einstein condensate of ^{41}K residing in a large Fermi sea of ^{6}Li. We quantify the residual spatial overlap between the two components by measuring three-body recombination losses for variable strength of the interspecies repulsion. A comparison with a numerical mean-field model highlights the importance of the kinetic energy term for the condensed bosons in maintaining the thin interface far into the phase-separated regime. Our results demonstrate a corresponding smoothing of the phase transition in a system of finite size.

arXiv:1802.01954•Physical Review Letters•Jun 13, 2018•75 citations

Quantum Droplets in a Resonant Bose-Fermi Mixture

Anonymous, O. Bleu, Jesper Levinsen +1 more

We study the canonical problem of a Fermi gas interacting with a weakly repulsive Bose-Einstein condensate at zero temperature. To explore the quantum phases across the full range of boson-fermion interactions, we construct a versatile variational Ansatz that incorporates pair correlations and correctly captures the different polaron limits. Remarkably, we find that self-bound quantum droplets can exist in the strongly interacting regime, preempting the formation of boson-fermion dimers, when the Fermi pressure is balanced by the resonant boson-fermion attraction. This scenario can be achieved in experimentally available Bose-Fermi mixtures for a range of boson-fermion mass ratios in the vicinity of equal masses. We furthermore show that a larger fermion density instead yields phase separation between a Bose-Fermi mixture and excess fermions, as well as behavior reminiscent of a liquid-gas critical point. Our results suggest that first-order quantum phase transitions play a crucial role in the phase diagram of Bose-Fermi mixtures.

arXiv:2601.12777•Physical Review Letters•Jul 8, 2026•1 citation

Spectral properties and breathing dynamics of a few-body Bose–Bose mixture in a 1D harmonic trap

Maxim Pyzh, Sven Krönke, Christof Weitenberg +1 more

We investigate a few-body mixture of two bosonic components, each consisting of two particles confined in a quasi one-dimensional harmonic trap. By means of exact diagonalization with a correlated basis approach we obtain the low-energy spectrum and eigenstates for the whole range of repulsive intra- and inter-component interaction strengths. We analyse the eigenvalues as a function of the inter-component coupling, covering hereby all the limiting regimes, and characterize the behaviour in-between these regimes by exploiting the symmetries of the Hamiltonian. Provided with this knowledge we study the breathing dynamics in the linear-response regime by slightly quenching the trap frequency symmetrically for both components. Depending on the choice of interactions strengths, we identify 1 to 3 monopole modes besides the breathing mode of the centre of mass coordinate. For the uncoupled mixture each monopole mode corresponds to the breathing oscillation of a specific relative coordinate. Increasing the inter-component coupling first leads to multi-mode oscillations in each relative coordinate, which turn into single-mode oscillations of the same frequency in the composite-fermionization regime.

arXiv:1707.03758•New Journal of Physics•Jan 11, 2018•24 citations

Collective excitations of a trapped boson-fermion mixture across demixing

P. Capuzzi, Anna Minguzzi, M. P. Tosi

We calculate the spectrum of low-lying collective excitations in a mesoscopic cloud formed by a Bose-Einstein condensate and a spin-polarized Fermi gas as a function of the boson-fermion repulsions. The cloud is under isotropic harmonic confinement and its dynamics is treated in the collisional regime by using the equations of generalized hydrodynamics with inclusion of surface effects. For large numbers of bosons, we find that as the cloud moves towards spatial separation (demixing) with increasing boson-fermion coupling, the frequencies of a set of collective modes show a softening followed by a sharp upturn. This behavior permits a clear identification of the quantum phase transition. We propose a physical interpretation for the dynamical transition point in a confined mixture, leading to a simple analytical expression for its location.

arXiv:cond-mat/0301522•Physical Review A•May 23, 2003•43 citations
We investigate the fundamental breathing mode of a small-sized elongated Bose-Einstein condensate coupled to a large Fermi sea, which consists of fully spin-polarized atoms in the collisionless regime. Our observations show a dramatic shift of the breathing frequency when the mixture undergoes phase separation at strong interspecies repulsion. We find that the maximum frequency shift in the full phase-separation limit depends essentially on the atom number ratio of the components. We interpret the experimental observations by modeling the complex dynamics of the collisionless fermions within two complementary approaches. One model assumes an adiabatic response of the Fermi sea, while the other one considers single fermion trajectories for a fully phase-separated mixture. Our models capture the observed features over the full range of interest.
By analyzing the breathing mode of a Bose-Einstein condensate repulsively interacting with a polarized fermionic cloud, we further the understanding of a Bose-Fermi mixture recently realized by Lous et al. [Phys. Rev. Lett. 120, 243403 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.243403]. We show that a hydrodynamic description of a domain wall between bosonic and fermionic atoms reproduces the experimental data of Huang et al. [Phys. Rev. A 99, 041602(R) (2019)PLRAAN2469-992610.1103/PhysRevA.99.041602]. Two different types of interaction renormalization are explored, based on lowest-order constrained variational and perturbation techniques. In order to replicate nonmonotonic behavior of the oscillation frequency observed in the experiment, temperature effects have to be included. We find that the frequency down-shift is caused by the fermion-induced compression and rethermalization of the bosonic species as the system is quenched into the strongly interacting regime.
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 41K^{41}\mathrm{K}41K and 6Li^{6}\mathrm{Li}6Li.
We probe the interface between a phase-separated Bose-Fermi mixture consisting of a small Bose-Einstein condensate of ^{41}K residing in a large Fermi sea of ^{6}Li. We quantify the residual spatial overlap between the two components by measuring three-body recombination losses for variable strength of the interspecies repulsion. A comparison with a numerical mean-field model highlights the importance of the kinetic energy term for the condensed bosons in maintaining the thin interface far into the phase-separated regime. Our results demonstrate a corresponding smoothing of the phase transition in a system of finite size.
We study the canonical problem of a Fermi gas interacting with a weakly repulsive Bose-Einstein condensate at zero temperature. To explore the quantum phases across the full range of boson-fermion interactions, we construct a versatile variational Ansatz that incorporates pair correlations and correctly captures the different polaron limits. Remarkably, we find that self-bound quantum droplets can exist in the strongly interacting regime, preempting the formation of boson-fermion dimers, when the Fermi pressure is balanced by the resonant boson-fermion attraction. This scenario can be achieved in experimentally available Bose-Fermi mixtures for a range of boson-fermion mass ratios in the vicinity of equal masses. We furthermore show that a larger fermion density instead yields phase separation between a Bose-Fermi mixture and excess fermions, as well as behavior reminiscent of a liquid-gas critical point. Our results suggest that first-order quantum phase transitions play a crucial role in the phase diagram of Bose-Fermi mixtures.
We investigate a few-body mixture of two bosonic components, each consisting of two particles confined in a quasi one-dimensional harmonic trap. By means of exact diagonalization with a correlated basis approach we obtain the low-energy spectrum and eigenstates for the whole range of repulsive intra- and inter-component interaction strengths. We analyse the eigenvalues as a function of the inter-component coupling, covering hereby all the limiting regimes, and characterize the behaviour in-between these regimes by exploiting the symmetries of the Hamiltonian. Provided with this knowledge we study the breathing dynamics in the linear-response regime by slightly quenching the trap frequency symmetrically for both components. Depending on the choice of interactions strengths, we identify 1 to 3 monopole modes besides the breathing mode of the centre of mass coordinate. For the uncoupled mixture each monopole mode corresponds to the breathing oscillation of a specific relative coordinate. Increasing the inter-component coupling first leads to multi-mode oscillations in each relative coordinate, which turn into single-mode oscillations of the same frequency in the composite-fermionization regime.
We calculate the spectrum of low-lying collective excitations in a mesoscopic cloud formed by a Bose-Einstein condensate and a spin-polarized Fermi gas as a function of the boson-fermion repulsions. The cloud is under isotropic harmonic confinement and its dynamics is treated in the collisional regime by using the equations of generalized hydrodynamics with inclusion of surface effects. For large numbers of bosons, we find that as the cloud moves towards spatial separation (demixing) with increasing boson-fermion coupling, the frequencies of a set of collective modes show a softening followed by a sharp upturn. This behavior permits a clear identification of the quantum phase transition. We propose a physical interpretation for the dynamical transition point in a confined mixture, leading to a simple analytical expression for its location.