Imaging FFLO Domain Walls in a Quasi-1D Spin-Imbalanced Fermi Gas

The Fulde-Ferrell Larkin-Ovchinnikov (FFLO) polarized superconductor is predicted to exhibit both superconducting and magnetic order. We explore this elusive state of matter using quantum simulation:  hyperfine sublevels of ⁶Li are stand-ins for the electrons, and a 2D optical lattice creates an array of quasi-1D tubes.  The excess spin-up atoms are expected to localize in periodic domain walls for the LO phase. We seek to directly image these domain walls via polarization phase contrast imaging (PPCI). We first load a degenerate sample of ⁶Li atoms into a 2D optical lattice with a very long aspect ratio, with a controllable spin-imbalance between two hyperfine levels. By varying the inter-tube tunneling rate via a Feshbach resonance and the lattice depth, it may be possible to lock the phase of the domain wall oscillations in adjacent tubes, and thus enabling coherent averaging the signal. By using FFT’s combined with data averaging techniques, we hope to reveal the periodic domain wall structure.