Abstract

We determine the exact dynamics of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultracold atoms in a deep hexagonal optical lattice. The dynamical evolution is triggered by a quench of the lattice potential such that the interaction strength U-f is much larger than the hopping amplitude J(f). The quench initiates collective oscillations with frequency vertical bar U-f vertical bar/2 pi in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the BCS order parameter Delta. The oscillation frequency of Delta is not reproduced by treating the time evolution in mean-field theory. In our theory, the momentum noise (i.e., density-density) correlation functions oscillate at frequency vertical bar U-f vertical bar/2 pi as well as at its second harmonic. For a very deep lattice, with zero tunneling energy, the oscillations of momentum occupation numbers are undamped. Nonzero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. The damping occurs even for a finite-temperature initial BCS state, but not for a noninteracting Fermi gas. Furthermore, damping is stronger for larger order parameter and may therefore be used as a signature of the BCS state. Finally, our theory shows that the noise correlation functions in a honeycomb lattice will develop strong anticorrelations near the Dirac point.

Publication Details
Publication Type
Journal Article
Year of Publication
2016
Volume
94
DOI
10.1103/PhysRevA.94.023607
Journal
Physical Review A
Contributors