Anisotropic Polarizability of Ultracold Polar $^{40}$K$^{87}$Rb   Molecules
  We report the measurement of the anisotropic AC polarizability of ultracold polar $^{40}$K$^{87}$Rb molecules in the ground and first rotationally excited states. Theoretical analysis of the polarizability agrees well with experimental findings. Although the polarizability can vary by more than 30%, a "magic" angle between the laser polarization and the quantization axis is found where the polarizability of the $|N=0,m_N=0>$ and the $|N=1,m_N=0>$ states match. At this angle, rotational decoherence due to the mismatch in trapping potentials is eliminated, and we observe a sharp increase in the coherence time. This paves the way for precise spectroscopic measurements and coherent manipulations of rotational states as a tool in the creation and probing of novel quantum many-body states of polar molecules. 
B. Neyenhuis, B. Yan, S. A. Moses, J. P. Covey, A. Chotia, A. Petrov,   S. Kotochigova, J. Ye, D. S. Jin
physics.atom-ph cond-mat.quant-gas quant-ph