Onset of dissipation of BEC in shaking 2D Anti-dot optical lattices

We present a series of experiments with 87\textasciicircum Rb BEC loaded into 2D anti-dot optical lattices. This lattice has periodically arranged potential hills and energy minima which are connected to be mesh-like structure. BEC in the lattice is considered to be well described as BEC with many holes when the barrier is slightly higher than chemical potential. We study onsets of dissipation of BEC by sinusoidally shaking anti-dot lattices. The dissipation is monitored by condensed fractions after thermalization. Below 0.5Erec barrier, we found a critical velocity vc, close to 0.5 recoil velocity. vc decrease down to $\sim$ 1mm/s at 2Erec and stay constant for much higher hills. The effects of dissipation also appear in interference patterns just after shaking. We present the details of our experiments.