We study the mean-field dynamic of a interacting boson-fermion mixture in an harmonic trap, by means of a Gaussian variational ansatz. We find concentric stationary solutions in the repulsive regime and in the regime of weak boson-fermion attraction. Above a threshold value of the repulsion parameter, a stable symmetry-broken stationary solution bifurcates, characterized by the displacement of the center of mass of the bosonic and fermionic clouds in opposite directions away from the trap center. We observe linear and nonlinear oscillations of the width and center of mass of the boson and fermion distributions whenever we let the system evolve starting from a non stationary initial condition. Advisor: Dr. Nicola Manini Co-Advisor: Dr. Luca Salasnich
We study the mean-field dynamic of a interacting boson-fermion mixture in an harmonic trap, by means of a Gaussian variational ansatz. We find concentric stationary solutions in the repulsive regime and in the regime of weak boson-fermion attraction. Above a threshold value of the repulsion parameter, a stable symmetry-broken stationary solution bifurcates, characterized by the displacement of the center of mass of the bosonic and fermionic clouds in opposite directions away from the trap center. We observe linear and nonlinear oscillations of the width and center of mass of the boson and fermion distributions whenever we let the system evolve starting from a non stationary initial condition. Advisor: Dr. Nicola Manini Co-Advisor: Dr. Luca Salasnich
We analyse the ground-state density profiles of a cloud of ultracold fermions in a harmonic, cilindrically symmetric potential. We study in detail the BCS-BEC crossover as the fermion-fermion interaction strength varies. We evaluate the ground-state wavefunction in a mean field regime, expanding the wavefunction on a truncated harmonic-oscillator basis of eigenfunctions. We use LAPACK routines to solve iteratively the nonlinear matrix problem; we study the convergence properties of this method with respect to the basis size. Advisor: Dr. Nicola Manini Co-Advisor: Dr. Luca Salasnich
We study formation of a Bose–Fermi droplet in realistic experimental setting. We start with a typical experimental arrangement of two atomic species—bosons and fermions in a harmonic axially symmetric confinement. The variational analysis shows that the system exhibits bistability. For weak repulsion between bosons, one of the equilibrium states, smaller in size, spherically symmetric, and with negative energy, corresponds to quantum droplet; the other with always positive energy represents the elongated droplet-like state immersed in the sea of a fermionic cloud. For stronger repulsion between bosons the bifurcation is seized and only the former state is left. Now it represents an elongated object which, for strong enough boson–fermion attraction, gets negative energy. It becomes an excited Bose–Fermi droplet when the trap is released, what is demonstrated by solving the quantum hydrodynamics equations for the Bose–Fermi system. To depict our ideas we consider the 133 Cs– 6 Li mixture under ideal conditions, i.e. we assume no losses.
In this paper, we study the interaction-modulated tunneling dynamics of a Bose-Fermi superfluid mixture, where a Bose-Einstein condensate (BEC) with weak repulsive interaction is confined in a symmetric deep double-well potential and an equally populated two-component Fermi gas in a harmonic potential symmetrically is positioned in the center of the double-well potential. The tunneling between the two wells is modulated by fermions trapped in a harmonic potential. When the temperature is adequately low and the bosonic particle number is adequately large, we can employ the mean-field theory to describe the evolution of the BEC in the double-well potential through the time-dependent Gross-Pitaevskii equation. For the Fermi gas in the harmonic potential trap, we consider the case where the inter-fermion interaction is tuned on the deep Bose-Einstein condensate of the inter-fermion Feshbach resonance, where two fermions of spin-up and spin-down form a two-body bound state. Within the regime, the Fermi gas is well described by a condensate of these fermionic dimers, and hence can be simulated as well by a Gross-Pitaevskii equation of dimers. The inter-species interactions couple the dynamics of the two species, which results in interesting features in the tunneling oscillations. The dynamic equations of the BEC in the double-well potential is described by a two-mode approximation. Coupling it with time-dependent Gross-Pitaevskii equation of the harmonically potential trapped molecular BEC, we numerically investigate the dynamical evolution of the Boson-Fermi hybrid system under different initial conditions. It is found that the interaction among fermions in a harmonic potential leads to strong non-linearity in the oscillations of the bosons in the double-well potential and enriches the tunneling dynamics of the bosons. Especially, it strengthens macroscopic quantum self-trapping. And the macroscopic quantum self-trapping can be expressed in three forms: the phase tends to be negative and monotonically decreases with time, the phase evolves with time, and the phase tends to be positive and increases monotonically with time. This means that it is possible the tunneling dynamics of the BEC in double-well potential is adjustable. Our results can be verified experimentally in a Bose-Fermi superfluid mixture by varying different interaction parameters via Feshbach resonance and confinement-induced resonance.
We consider a one-dimensional interacting Bose-Fermi mixture with equal masses of bosons and fermions, and with equal and repulsive interactions between Bose-Fermi and Bose-Bose particles. Such a system can be realized in experiments with ultracold boson and fermion isotopes in optical lattices. We use the Bethe-ansatz technique to find the ground state energy at zero temperature for any value of interaction strength and density ratio between bosons and fermions. We prove that the mixture is always stable against demixing. Combining exact solution with the local density approximation, we calculate density profiles and collective oscillation modes in a harmonic trap. In the strongly interating regime, we use exact wave functions to calculate correlation functions for bosons and fermions under periodic boundary conditions.
A solvable model of a generic trapped bosonic mixture, N 1 bosons of mass m 1 and N 2 bosons of mass m 2 trapped in an harmonic potential of frequency ω and interacting by harmonic inter-particle interactions of strengths λ 1 , λ 2 , and λ 12 , is discussed. It has recently been shown for the ground state [J. Phys. A 50 , 295002 (2017)] that in the infinite-particle limit, when the interaction parameters λ 1 ( N 1 − 1), λ 2 ( N 2 − 1), λ 12 N 1 , λ 12 N 2 are held fixed, each of the species is 100% condensed and its density per particle as well as the total energy per particle are given by the solution of the coupled Gross-Pitaevskii equations of the mixture. In the present work we investigate properties of the trapped generic mixture at the infinite-particle limit, and find differences between the many-body and mean-field descriptions of the mixture, despite each species being 100%. We compute analytically and analyze, both for the mixture and for each species, the center-of-mass position and momentum variances, their uncertainty product, the angular-momentum variance, as well as the overlap of the exact and Gross-Pitaevskii wavefunctions of the mixture. The results obtained in this work can be considered as a step forward in characterizing how important are many-body effects in a fully condensed trapped bosonic mixture at the infinite-particle limit.
We investigate theoretically the behavior of a one-dimensional interacting Bose-Fermi mixture with equal masses and equal repulsive interactions between atoms at finite temperature in the scheme of thermodynamic Bethe ansatz. Combining the Yang-Yang thermodynamic formalism with local-density approximation in a harmonic trap, we calculate the density distribution of bosons and fermions numerically by treating the radially and axially excited states as discrete and continuous ones, respectively. Our result from exactly solvable solutions may be used as a touchstone for one-dimensional interacting Bose-Fermi mixture for experimental data fitting where mean-field theoretical approaches fail.