Figure 1

Integrated density profiles of an imbalanced Fermi gas. Blue (dark gray): majority atoms ${\overline{n}}_1(z)$; Red (medium gray): minority atoms ${\overline{n}}_2(z)$; Green (light gray): difference ${\overline{n}}_d={\overline{n}}_1-{\overline{n}}_2$. In this latter case, the flat-top feature signals a cancellation of the density difference at the center of the trap, characteristic of the existence of a fully paired superfluid core. The superfluid (resp. minority) radius $R_S$ (resp. $R_2$) are marked by vertical dashed lines. The solid color lines correspond to the prediction of Monte Carlo theories [20], the only fit parameters being the number of atoms in each spin state, $N_1=8.0\times {10}^4$, $N_2=2.4\times {10}^4$ for this image. The axial (radial) trap frequency is 18.6 Hz (420 Hz).Reuse & Permissions

Figure 2

(a) Oscillations of the axial radius of the majority component, for a population imbalance $P=0.85(2)$, beyond the Clogston limit. The solid line corresponds to a fit by an exponentially damped sinusoid. (b) Frequency of the breathing mode ${\omega }_1$ normalized to the axial trapping frequency ${\omega }_z$ versus polarization. The superfluid (resp. collisionless) limits ${\omega }_1=\sqrt{12/5}{\omega }_z$ (resp. $2{\omega }_z$) are indicated by the dashed red lines. The axial (radial) trap frequency is 28.9(1) Hz (420 Hz). (c) Damping rate ${\gamma }_1$ versus polarization (in log scale). Note that our data are limited to $P<0.95$ due to the small minority atom number ($N_2\lesssim 2\times {10}^3$) at such high polarizations.Reuse & Permissions

Figure 3

Comparison of our experimental results with the parametric curve (${\omega }_1(\tau )/{\omega }_z$, ${\gamma }_1(\tau )/{\omega }_1(\tau )$) deduced from prediction (4). The data in blue (dark gray) [red (medium gray)] correspond to polarizations $P<0.8$ [$P>0.8$].Reuse & Permissions

Figure 4

(a) Frequency power spectrum of the minority spin state for $P=0.90(2)$. The peak between ${\omega }_{\mathrm{HD}}$ and ${\omega }_{\mathrm{CL}}$ corresponds to the oscillation in phase with the majority, the other one to the polaron oscillation. (b) Frequency of the polaron component as a function of polarization. All frequencies are normalized to ${\omega }_z$.Reuse & Permissions