Radio-Frequency Spectroscopy of a Strongly Interacting Two-Dimensional Fermi Gas

We realize and study a strongly interacting two-component atomic Fermi gas confined to two dimensions in an optical lattice. Using radio-frequency spectroscopy we measure the interaction energy of the strongly interacting gas. We observe the confinement-induced Feshbach resonance on the attractive side of the 3D Feshbach resonance and find the existence of confinement-induced molecules in very good agreement with theoretical predictions.

Figure 1

Radio-frequency spectrum showing the characteristic two-peak structure of the atomic peak (right), shifted by the interaction energy, and the molecular peak (left). The solid line shows a double Lorentzian fit to extract the peak positions. The spectrum is recorded at 225 G in an optical lattice of $83E_{\mathrm{rec}}$ depth.

Figure 2

Measurement of the interaction energy shift of a two-dimensional Fermi gas in an optical lattice of $83E_{\mathrm{rec}}$. The data points show the measured frequency shift as compared to the atomic Zeeman energy. The solid line shows the expected energy shift in the weak-coupling regime, the dashed line shows its continuation into the strongly interacting regime. The vertical line indicates the position of the three-dimensional Feshbach resonance at $224.20\pm 0.03\mathrm{G}$. We determine the confinement-induced resonance at $224.72\pm 0.05\mathrm{G}$. The inset shows the measurement for a three-dimensional Fermi gas. Error bars indicate the fitting errors in determining the peak of the spectrum.

Figure 3

(a) Location of the confinement-induced Feshbach resonance vs depth of the optical lattice. The solid line is the prediction of Eq. (1) without free parameters. (b) Slope of the interaction energy at the zero-crossing of the confinement-induced resonance. The data points at zero lattice depth in both graphs show the result for the three-dimensional Feshbach resonance. The value of $224.20\pm 0.03\mathrm{G}$ is in excellent agreement with [23].

Figure 4

(a) Binding energy of confinement-induced molecules at a lattice depth of $83E_{\mathrm{rec}}$. The dashed line is the prediction of Eq. (2). The solid line is the same curve offset by 4 kHz to fit the experimental data. (b) Binding energy of the confinement-induced molecules at the location of the three-dimensional Feshbach resonance at 224.2 G. The line is a linear fit to the data.