Fermi Gases in Slowly Rotating Traps: Superfluid versus Collisional Hydrodynamics

The dynamic behavior of a Fermi gas confined in a deformed trap rotating at low angular velocity is investigated in the framework of hydrodynamic theory. The differences exhibited by a normal gas in the collisional regime and a superfluid are discussed. Special emphasis is given to the collective oscillations excited when the deformation of the rotating trap is suddenly removed or when the rotation is suddenly stopped. The presence of vorticity in the normal phase is shown to give rise to precession and beating phenomena which are absent in the superfluid phase.

Figure 1

Time evolution of the angle $\theta$ (measured in radians and plotted modulus $\pi /2$) after the sudden switching off of the trap deformation. (a) Superfluid hydrodynamics; (b) collisional hydrodynamics. The trap parameters are $ϵ=0.2$, $\Omega =0.2{\omega }_{\perp }$, ${\omega }_z/{\omega }_{\perp }=0.1$, while $\gamma =2/3$. The dashed line in (b) is the curve $\theta =\Omega t/2$ (see text).

Figure 2

Time evolution of the angle $\theta$ (measured in degrees) after the sudden stop of the rotation of the trap. (a) Superfluid hydrodynamics; (b) collisional hydrodynamics. Parameters as in Fig. 1.