



01747nas a2200157   4500008004100000245008800041210006900129260001500198300001100213490000700224520127000231100001801501700001501519700001901534856003601553       2016                        eng d00aSudden-quench dynamics of Bardeen-Cooper-Schrieffer states in deep optical lattices0 aSuddenquench dynamics of BardeenCooperSchrieffer states in deep   c2016/08/05  a0236070 v943 a<p>We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency |Uf|/(2π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency |Uf|/2π as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point.</p>1 aNuske, Marlon1 aMathey, L.1 aTiesinga, Eite  uhttp://arxiv.org/abs/1602.0097901328nas a2200157   4500008004100000245008400041210006900125260001500194300001100209490000700220520085400227100001801081700001901099700001501118856003701133       2015                        eng d00aOptimization of collisional Feshbach cooling of an ultracold  nondegenerate gas0 aOptimization of collisional Feshbach cooling of an ultracold non  c2015/04/20  a0436260 v913 a  We optimize a collision-induced cooling process for ultracold atoms in the
nondegenerate regime. It makes use of a Feshbach resonance, instead of rf
radiation in evaporative cooling, to selectively expel hot atoms from a trap.
Using functional minimization we analytically show that for the optimal cooling
process the resonance energy must be tuned such that it linearly follows the
temperature. Here, optimal cooling is defined as maximizing the phase-space
density after a fixed cooling duration. The analytical results are confirmed by
numerical Monte-Carlo simulations. In order to simulate more realistic
experimental conditions, we show that background losses do not change our
conclusions, while additional non-resonant two-body losses make a lower initial
resonance energy with non-linear dependence on temperature preferable.
1 aNuske, Marlon1 aTiesinga, Eite1 aMathey, L.  uhttp://arxiv.org/abs/1412.8473v1