Raman-Induced Interactions in a Single-Component Fermi Gas Near an $s$-Wave Feshbach Resonance

Ultracold gases of interacting spin-orbit-coupled fermions are predicted to display exotic phenomena such as topological superfluidity and its associated Majorana fermions. Here, we experimentally demonstrate a route to strongly interacting single-component atomic Fermi gases by combining an $s$-wave Feshbach resonance (giving strong interactions) and spin-orbit coupling (creating an effective $p$-wave channel). We identify the Feshbach resonance by its associated atomic loss feature and show that, in agreement with our single-channel scattering model, this feature is preserved and shifted as a function of the spin-orbit-coupling parameters.

Figure 1

(a),(c) Counterpropagating Raman beams couple two hyperfine spin states in ${}^{40}\mathrm{K}$’s electronic ground state. (b) Energy bands for $\hslash \Omega =2E_R$ and $\delta =0$. The color indicates the relative amplitude of the bare spin states in the dressed superposition. (d) Binding energy near the ${}^{40}\mathrm{K}$ Feshbach resonance. (e) Two-body energies showing the lowest band shift below the bare continuum for center-of-mass momentum $q_{\mathrm{c}.\mathrm{m}.}=0$ and relative momentum $q_1-q_2=2\delta q$ for $\hslash \Omega =8E_R$ and $\delta =0$. The upper and lower Raman-dressed bands are denoted using $|+⟩$ and $|-⟩$, respectively. (f) Center of loss feature versus Raman coupling strength $\Omega$ with a large two-photon detuning ($\hslash \delta =36E_R$) illuminating an incoherent spin mixture.

Figure 2

(a) Atom number as a function of magnetic field for $\hslash \Omega =4.7E_R$ and detunings $\delta$: gray, $\hslash \delta =0$; red, $\hslash \delta =2.4E_R$; blue, $\hslash \delta =4.7E_R$; green, $\hslash \delta =5.9E_R$; orange, $\hslash \delta =7.1E_R$; magenta, $\hslash \delta =8.3E_R$. The solid curves are Gaussian fits to the data. (b) Center of loss feature as a function of $\delta$. (c) Fraction of atoms lost as a function of $\delta$. Uncertainty bars represent 1 standard deviation.

Figure 3

Predicted energy of the last bound molecular state as a function of (a) Raman coupling strength $\Omega$ for $\delta =0$ and (b) $\delta$ for $\hslash \Omega =4.7E_R$. The color scale indicates the energy of the last bound state with center-of-mass momentum $\hslash q_{\mathrm{c}.\mathrm{m}.}$, and the white region denotes where the bound state has entered the continuum and becomes a scattering state. The red curve denotes the prediction of the simple model discussed in the text. Experimental data, with the background shift of Fig. 1f subtracted, is shown by the black circles.

Figure 4

Atom number versus hold time in an optical dipole trap for different scenarios: (i) gray squares, $B=201.9\mathrm{G}$, $\hslash \Omega =2.1E_R$, $\hslash \delta =33E_R$, (ii) blue circles, $B=201.9\mathrm{G}$, $\hslash \Omega =2.1E_R$, $\hslash \delta =0$. Inset: The data of (ii) plotted as $1/N$. The linear time dependence of $1/N$ is consistent with a two-body decay process.