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J. Radogostowicz1, A. Zenesini1, H. Lignier1, G. Tayebirad 4 , C. Sias2, M.Viteau1, D. Ciampini1, M. Jona-Lasinio3, R. Mannella 1 ,S. Wimberger4, O. Morsch1, E. Arimondo1 1. Pisa, Dipartamento di Fisica "E. Fermi", L.go. B. Pontecorvo 3, 56127 Pisa 2. Cavendish Laboratory, University of Cambridge, Cambridge CB3B 0HE, UK 3. LENS, Via N. Carrara 1, 50019 - Sesto Fiorentino, Italy 4. Universität Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany Landau Zener tunneling is an example of a simple tunneling problem in which a quantum particle tunnels through the energy gap at an avoided crossing between two energy levels of the system. We present experimental and numerical results for deviations from the simple results of Landau Zener theory in the case of asymmetric tunneling in the presence of interactions as well as for "interrupted" tunneling events representing a time-resolved measurement of the Landau-Zener process. We investigated the case of Landau Zener tunneling in the presence of nonlinearity which leads to an asymmetric tunnelling rate (probability of tunnelling from one band to another) [1]. An enhancement of the tunnelling probability occurs when the atoms tunnel from the lower to the upper band while tunnelling is suppressed in the opposite direction. The time resolved experiments were performed in both the diabatic and adiabatic bases of the problem, i.e., in the basis of the free particle states and in the band structure, respectively. The aim was to investigate the survival probability of a BEC initially loaded into the lowest band of the 1D optical lattice as a function of its position in the Brillouin zone [2]. In both bases we could observe a step-like discontinuous decay of the population in the ground state after part of them had tunnelled to the upper band. The measurements in the diabatic basis also showed strong oscillations in the survival probability. [1] M. Jona-Lasino et al. Phys. Rev. Lett. 91, 230406 (2003) [2] A.Zenesini et al. arXiv:0903.3345 (2009) |
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