We report on the observation of Bragg diffraction of a spin-polarized ultracold $^{6}\mathrm{Li}$ Fermi gas and demonstrate a Ramsey-type matter-wave interferometer. Suppression of $s$ -wave collisions by the Pauli principle allows for unperturbed dynamics of the atoms in the trap for longer than $2\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ . Employing an echo pulse sequence, we observe coherent superpositions of momentum states which do not show any sign of decoherence during the experimentally limited observation time of $100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$. In contrast, significant decoherence is observed in the presence of a cold cloud of $^{87}\mathrm{Rb}$ atoms. The experiment demonstrates the feasibility of high-resolution atomic interferometry with applications for precision measurements in small volumes and near surfaces.We report on the observation of Bragg diffraction of a spin-polarized ultracold $^{6}\mathrm{Li}$ Fermi gas and demonstrate a Ramsey-type matter-wave interferometer. Suppression of $s$-wave collisions by the Pauli principle allows for unperturbed dynamics of the atoms in the trap for longer than $2\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. Employing an echo pulse sequence, we observe coherent superpositions of momentum states which do not show any sign of decoherence during the experimentally limited observation time of $100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$. In contrast, significant decoherence is observed in the presence of a cold cloud of $^{87}\mathrm{Rb}$ atoms. The experiment demonstrates the feasibility of high-resolution atomic interferometry with applications for precision measurements in small volumes and near surfaces.

arXiv:0804.0532Physical Review AAug 12, 20085 citations

Bragg spectroscopy of cold atomic Fermi gases

Georg M. Bruun, Gordon Baym

We propose a Bragg spectroscopy experiment to measure the onset of superfluid pairing in ultracold trapped Fermi gases. In particular, we study two-component Fermi gases in the weak coupling BCS and Bose Einstein condensation limits as well as in the strong coupling unitarity limit. The low-temperature Bragg spectrum exhibits a gap directly related to the pair-breaking energy. Furthermore, the Bragg spectrum has a large maximum just below the critical temperature when the gas is superfluid in the BCS limit. In the unitarity regime, we show how the pseudogap in the normal phase leads to a significant suppression of the low-frequency Bragg spectrum.We propose a Bragg spectroscopy experiment to measure the onset of superfluid pairing in ultracold trapped Fermi gases. In particular, we study two-component Fermi gases in the weak coupling BCS and Bose Einstein condensation limits as well as in the strong coupling unitarity limit. The low-temperature Bragg spectrum exhibits a gap directly related to the pair-breaking energy. Furthermore, the Bragg spectrum has a large maximum just below the critical temperature when the gas is superfluid in the BCS limit. In the unitarity regime, we show how the pseudogap in the normal phase leads to a significant suppression of the low-frequency Bragg spectrum.

arXiv:cond-mat/0607334Physical Review ASep 29, 200635 citations

We report on the observation of Bragg diffraction of a spin-polarized ultracold

^{6}\mathrm{Li}

Fermi gas and demonstrate a Ramsey-type matter-wave interferometer. Suppression of

s

-wave collisions by the Pauli principle allows for unperturbed dynamics of the atoms in the trap for longer than

2\phantom{\rule{0.3em}{0ex}}\mathrm{s}

. Employing an echo pulse sequence, we observe coherent superpositions of momentum states which do not show any sign of decoherence during the experimentally limited observation time of $100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$. In contrast, significant decoherence is observed in the presence of a cold cloud of

^{87}\mathrm{Rb}

atoms. The experiment demonstrates the feasibility of high-resolution atomic interferometry with applications for precision measurements in small volumes and near surfaces.