Probing ultracold Fermi gases with light-induced gauge potentials

We theoretically investigate the response of a two-component Fermi gas to vector potentials that couple separately to the two spin components. Such vector potentials may be implemented in ultracold atomic gases using optically dressed states. Our study indicates that light-induced gauge potentials may be used to probe the properties of the interacting ultracold Fermi gas, providing, among other things, ways to measure the superfluid density and the strength of pairing.

Figure 1

Response function $\chi$ divided by ${\omega }^2$ as a function of $\frac{\omega }{\Delta }$ in the region $0⩽\omega <2\Delta$. Normalisation is with respect to the response of a noninteracting gas, $N/2m$. The interaction strength is given by $k_F{a}_s=-1.1$, where $a_s=\frac{\mathit{mV}}{4\pi \hslash {}^2}$ is the $s$-wave scattering length. The parameter $a=\frac{\mu }{\Delta }$ is given by $a=3.7$ and $r=1.0$. (Solid line) $\frac{\chi (\omega )}{{\omega }^2}$ as obtained by numerically integrating the expression in Eq.  (21). (Dashed line) Expression obtained from Eq.  (25).

Figure 2

Real and imaginary part of the response function for $T=0$ as a function of $\frac{\omega }{\Delta }$ for the same system as in Fig. 1. In the limit $\eta \to 0$, there is an infinitely sharp peak at $\omega =2\Delta$. For $\omega \gg 2\Delta$, the real part of the response is independent of $\omega$ and is given by Eq. (30).

Figure 3

Response as a function of $\frac{T}{T_c}$ both below and above $T_c$ for the same system as in Fig.  1. Normalization is with respect to the response of a noninteracting gas ($N/2m$). The kink in the response function occurs at $T=T_c$.