## SCL Seminar by Antun Balaz

Scientific Computing Laboratory seminar will be held on Friday, 28 October 2016 at 14:00 in “Dr. Dragan Popović” library reading room of the Institute of Physics Belgrade. The talk entitled

will be given by Dr Antun Balaž (Scientific Computing Laboratory, Institute of Physics Belgrade).

We will discuss conditions for order and chaos in the dynamics of an interacting Bose-Einstein condensate (BEC) confined by an external trap cut off by a hard-wall box potential [1]. The BEC is stirred by a laser to induce excitations manifesting as irregular spatial and energy oscillations of the trapped cloud. Adding laser stirring to the external trap results in an effective time-varying trapping frequency in connection with the dynamically changing external plus laser potential trap. The resulting dynamics will be analyzed numerically [2-5] by plotting the corresponding trajectories in coordinate, phase, and energy space. We also compute the Lyapunov exponents to confirm the existence of chaos in energy space. We will identify quantum effects and trap anharmonicity as main culprits for emergence of chaos in the system. However, the presence of chaos in energy space does not necessarily translate into chaos in coordinate space. In general, time-varying trapping frequency is found to promote chaos in a trapped BEC. On the other hand, we find that a suppression of chaos in a trapped BEC can be achieved by increasing the characteristic scale of the external trap with respect to the condensate size.

[1] R. R. Sakhel, et. al., Eur. Phys. J. D 70, 66 (2016).

[2] D. Vudragović, et. al., Comput. Phys. Commun. 183, 2021 (2012).

[3] V. Lončar, et. al., Comput. Phys. Commun. 200, 406 (2016).

[4] B. Satarić, et. al., Comput. Phys. Commun. 200, 411 (2016).

[5] V. Lončar, et. al., Comput. Phys. Commun. 209, 190 (2016).

**"Order and chaos in BEC dynamics "**will be given by Dr Antun Balaž (Scientific Computing Laboratory, Institute of Physics Belgrade).

**Abstract of the talk:**We will discuss conditions for order and chaos in the dynamics of an interacting Bose-Einstein condensate (BEC) confined by an external trap cut off by a hard-wall box potential [1]. The BEC is stirred by a laser to induce excitations manifesting as irregular spatial and energy oscillations of the trapped cloud. Adding laser stirring to the external trap results in an effective time-varying trapping frequency in connection with the dynamically changing external plus laser potential trap. The resulting dynamics will be analyzed numerically [2-5] by plotting the corresponding trajectories in coordinate, phase, and energy space. We also compute the Lyapunov exponents to confirm the existence of chaos in energy space. We will identify quantum effects and trap anharmonicity as main culprits for emergence of chaos in the system. However, the presence of chaos in energy space does not necessarily translate into chaos in coordinate space. In general, time-varying trapping frequency is found to promote chaos in a trapped BEC. On the other hand, we find that a suppression of chaos in a trapped BEC can be achieved by increasing the characteristic scale of the external trap with respect to the condensate size.

[1] R. R. Sakhel, et. al., Eur. Phys. J. D 70, 66 (2016).

[2] D. Vudragović, et. al., Comput. Phys. Commun. 183, 2021 (2012).

[3] V. Lončar, et. al., Comput. Phys. Commun. 200, 406 (2016).

[4] B. Satarić, et. al., Comput. Phys. Commun. 200, 411 (2016).

[5] V. Lončar, et. al., Comput. Phys. Commun. 209, 190 (2016).