Eur. Phys. J. Special Topics 217, 121-133 (2013)
https://doi.org/10.1140/epjst/e2013-01761-y

Regular Article

Double transfer through Dirac points in a tunable honeycomb optical lattice

¹ Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland
² LP2N - UMR 5298, Université Bordeaux 1, IOGS, CNRS, Institut d'Optique d'Aquitaine, Allée René Laroumagne, 33400 Talence, France
³ Theoretische Physik, ETH Zurich, 8093 Zurich, Switzerland

^a e-mail: uehlinger@phys.ethz.ch

Received: 2 October 2012
Revised: 15 January 2013
Published online: 11 March 2013

Abstract

We report on Bloch-Zener oscillations of an ultracold Fermi gas in a tunable honeycomb lattice. The quasi-momentum distribution of the atoms is measured after sequentially passing through two Dirac points. We observe a double-peak feature in the transferred fraction to the second band, both as a function of the band gap at the Dirac points and the quasi-momentum of the trajectory. Our results are in good agreement with a simple analytical model based on two successive Landau-Zener transitions. Owing to the variation of the potential gradient over the cloud size, coherent Stückelberg oscillations are not visible in our measurements. This effect of the harmonic confinement is confirmed by a numerical simulation of the dynamics of a trapped 2D system.