Transition to hydrodynamics in colliding fermion clouds

We study the transition from the collisionless to the hydrodynamic regime in a two-component spin-polarized mixture of 40 K atoms by exciting its dipolar oscillation modes inside harmonic traps. The time evolution of the mixture is described by the Vlasov–Landau equations and numerically solved with a fully three-dimensional concurrent code. We observe a master/slave behaviour of the oscillation frequencies depending on the dipolar mode that is excited. Regardless of the initial conditions, the transition to hydrodynamics is found to shift to lower values of the collision rate as the temperature decreases.We study the transition from the collisionless to the hydrodynamic regime in a two-component spin-polarized mixture of 40 K atoms by exciting its dipolar oscillation modes inside harmonic traps. The time evolution of the mixture is described by the Vlasov–Landau equations and numerically solved with a fully three-dimensional concurrent code. We observe a master/slave behaviour of the oscillation frequencies depending on the dipolar mode that is excited. Regardless of the initial conditions, the transition to hydrodynamics is found to shift to lower values of the collision rate as the temperature decreases.

arXiv:cond-mat/0310644Journal of Physics B Atomic Molecular and Optical PhysicsMar 24, 200413 citations

Transition to hydrodynamics in colliding fermion clouds : Theory of quantum gases and quantum coherence

Francesco Toschi, P. Capuzzi, Sauro Succi A +2 more

We study the transition from the collisionless to the hydrodynamic regime in a two-component spin-polarized mixture of 40 K atoms by exciting its dipolar oscillation modes inside harmonic traps. The time evolution of the mixture is described by the Vlasov-Landau equations and numerically solved with a fully three-dimensional concurrent code. We observe a master/slave behaviour of the oscillation frequencies depending on the dipolar mode that is excited. Regardless of the initial conditions, the transition to hydrodynamics is found to shift to lower values of the collision rate as the temperature decreases.We study the transition from the collisionless to the hydrodynamic regime in a two-component spin-polarized mixture of 40 K atoms by exciting its dipolar oscillation modes inside harmonic traps. The time evolution of the mixture is described by the Vlasov-Landau equations and numerically solved with a fully three-dimensional concurrent code. We observe a master/slave behaviour of the oscillation frequencies depending on the dipolar mode that is excited. Regardless of the initial conditions, the transition to hydrodynamics is found to shift to lower values of the collision rate as the temperature decreases.

Journal of Physics B Atomic Molecular and Optical PhysicsJan 1, 20040 citations

Collective excitations of quasi-two-dimensional trapped dipolar fermions: Transition from collisionless to hydrodynamic regime

Mehrtash Babadi, Eugene Demler

We study the collective excitations of polarized single-component quasi-two-dimensional dipolar fermions in an isotropic harmonic trap by solving the collisional Boltzmann-Vlasov (CBV) equation via the method of moments. We study the response to monopole and quadrupole perturbations of the trap potential and investigate the dynamical character of excitations in each case. Simple analytic formulas are found using the linearized scaling ansatz approximation and accurate numerical results are obtained by satisfying the first eight moments of the CBV equation. Except for the lowest-lying monopole mode that is weakly affected by collisions, the quadrupole and the higher-order monopole modes undergo a transition from the collisionless regime to a dissipative crossover regime and finally approach the hydrodynamic regime upon increasing the dipolar interaction strength. For strong transverse confinement (2D limit), we predict the existence of a temperature window within which the characteristics of the collective modes become temperature independent. This plateau, which is a direct consequence of dipole-dipole scatterings, persists as long as the scattering energies remain in the near-threshold regime. The predictions of this work are expected to be observable in the current experiments.We study the collective excitations of polarized single-component quasi-two-dimensional dipolar fermions in an isotropic harmonic trap by solving the collisional Boltzmann-Vlasov (CBV) equation via the method of moments. We study the response to monopole and quadrupole perturbations of the trap potential and investigate the dynamical character of excitations in each case. Simple analytic formulas are found using the linearized scaling ansatz approximation and accurate numerical results are obtained by satisfying the first eight moments of the CBV equation. Except for the lowest-lying monopole mode that is weakly affected by collisions, the quadrupole and the higher-order monopole modes undergo a transition from the collisionless regime to a dissipative crossover regime and finally approach the hydrodynamic regime upon increasing the dipolar interaction strength. For strong transverse confinement (2D limit), we predict the existence of a temperature window within which the characteristics of the collective modes become temperature independent. This plateau, which is a direct consequence of dipole-dipole scatterings, persists as long as the scattering energies remain in the near-threshold regime. The predictions of this work are expected to be observable in the current experiments.

arXiv:1209.3863Physical Review ADec 28, 201223 citations

Dynamics of trapped fermion clouds

Federico Toschi, Patrizia Vignolo, P. Capuzzi +2 more

Experiments at JILA on the collisions between two oscillating spin-polarized components of a Fermi gas of 40K atoms have shown that this setup is an important tool for studying the dynamics of quantum gases. We have developed advanced numerical methods to solve the Vlasov–Landau equations for a binary mixture of atomic Fermi gases inside a harmonic trap at very low temperatures. In particular, a locally adaptive importance-sampling technique allows us to handle collisional interactions several orders of magnitude more efficiently than in standard Monte Carlo calculations. These methods have been applied to study the dynamical and transport properties of a fermion mixture in the presence of mean-field interactions and of collisions between its components for system parameters ranging from the collisionless to the hydrodynamic regime.Experiments at JILA on the collisions between two oscillating spin-polarized components of a Fermi gas of 40K atoms have shown that this setup is an important tool for studying the dynamics of quantum gases. We have developed advanced numerical methods to solve the Vlasov–Landau equations for a binary mixture of atomic Fermi gases inside a harmonic trap at very low temperatures. In particular, a locally adaptive importance-sampling technique allows us to handle collisional interactions several orders of magnitude more efficiently than in standard Monte Carlo calculations. These methods have been applied to study the dynamical and transport properties of a fermion mixture in the presence of mean-field interactions and of collisions between its components for system parameters ranging from the collisionless to the hydrodynamic regime.

Laser PhysicsJan 1, 20040 citations

Dynamics of trapped two-component Fermi gas: Temperature dependence of the transition from collisionless to collisional regime

Federico Toschi, Patrizia Vignolo, Sauro Succi A +1 more

We develop a numerical method to study the dynamics of a two-component atomic Fermi gas trapped inside a harmonic potential at temperature T well below the Fermi temperature ${T}_{F}.$ We examine the transition from the collisionless to the collisional regime down to $T=0.2{T}_{F}$ and find a good qualitative agreement with the experiments of B. DeMarco and D.S. Jin [Phys. Rev. Lett. 88, 040405 (2002)]. We demonstrate a twofold role of temperature on the collision rate and on the efficiency of collisions. In particular, we observe a hitherto unreported effect, namely, the transition to hydrodynamic behavior is shifted towards lower collision rates as temperature decreases.We develop a numerical method to study the dynamics of a two-component atomic Fermi gas trapped inside a harmonic potential at temperature T well below the Fermi temperature ${T}_{F}.$ We examine the transition from the collisionless to the collisional regime down to $T=0.2{T}_{F}$ and find a good qualitative agreement with the experiments of B. DeMarco and D.S. Jin [Phys. Rev. Lett. 88, 040405 (2002)]. We demonstrate a twofold role of temperature on the collision rate and on the efficiency of collisions. In particular, we observe a hitherto unreported effect, namely, the transition to hydrodynamic behavior is shifted towards lower collision rates as temperature decreases.

arXiv:cond-mat/0210577Physical Review AApr 25, 200326 citations

Dipole oscillation of a trapped Bose-Fermi-mixture gas in collisionless and hydrodynamic regimes

Yoji Asano, Shohei Watabe, Tetsuro Nikuni

Dipole oscillation is studied in a normal phase of a trapped Bose-Fermi-mixture gas composed of single-species bosons and single-species fermions. Applying the moment method to the linearized Boltzmann equation, we derive a closed set of equations of motion for the center-of-mass position and momentum of both components. By solving the coupled equations, we reveal the behavior of dipole modes in the transition between the collisionless regime and the hydrodynamic regime. We find that two oscillating modes in the collisionless regime have distinct fates in the hydrodynamic regime: one collisionless mode shows a crossover to a hydrodynamic in-phase mode, and the other collisionless mode shows a transition to two purely damped modes. The temperature dependence of these dipole modes are also discussed.Dipole oscillation is studied in a normal phase of a trapped Bose-Fermi-mixture gas composed of single-species bosons and single-species fermions. Applying the moment method to the linearized Boltzmann equation, we derive a closed set of equations of motion for the center-of-mass position and momentum of both components. By solving the coupled equations, we reveal the behavior of dipole modes in the transition between the collisionless regime and the hydrodynamic regime. We find that two oscillating modes in the collisionless regime have distinct fates in the hydrodynamic regime: one collisionless mode shows a crossover to a hydrodynamic in-phase mode, and the other collisionless mode shows a transition to two purely damped modes. The temperature dependence of these dipole modes are also discussed.

arXiv:1909.10178Physical Review AJan 13, 20205 citations

We develop a numerical method to study the dynamics of a two-component atomic Fermi gas trapped inside a harmonic potential at temperature T well below the Fermi temperature

{T}_{F}.

We examine the transition from the collisionless to the collisional regime down to

T=0.2{T}_{F}

and find a good qualitative agreement with the experiments of B. DeMarco and D.S. Jin [Phys. Rev. Lett. 88, 040405 (2002)]. We demonstrate a twofold role of temperature on the collision rate and on the efficiency of collisions. In particular, we observe a hitherto unreported effect, namely, the transition to hydrodynamic behavior is shifted towards lower collision rates as temperature decreases.