Dynamic response of strongly correlated Fermi gases in the quantum virial expansion

By developing a quantum virial expansion theory, we quantitatively calculate the dynamic density response function of a trapped strongly interacting Fermi gas at high temperatures near unitarity. A clear transition from atomic to molecular responses is identified in the spectra when crossing from the BCS to BEC regimes, in qualitative agreement with recent Bragg spectroscopy observations. Our virial expansion method provides a promising way to solve the challenging strong-coupling problems and is applicable to other dynamical properties of strongly correlated Fermi gases.

Figure 1

Evolution of the density structure factor with increasing interaction strength $~$ at $0.2T_F$ (a) and $1/k_{F}a$ (b). The inset in (b) shows the peak position as a function of $T=0.5T_F$.

Figure 2

$T=T_F$ (dashed lines) and $1/k_{F}a$ (solid lines) at different interaction strengths and at $S_{\uparrow \uparrow }(\mathbf{q},\omega )$ (left column) and $S_{\uparrow \downarrow }(\mathbf{q},\omega )$ (right column).

Figure 3

Temperature dependence of $T=0.5T_F$ at unitarity. The inset shows the red shift of the total dynamic structure factor with decreasing temperature.

Figure 4

Dependence of static structure factors on the momentum (a) and interaction strength (b) at $T=T_F$.