Manipulating quantum states with aspheric lenses
  We present an experimental demonstration to manipulate the width and position of the down-converted beam waist. Our results can be used to engineer the two-photon orbital angular momentum (OAM) entangled states (such as concentrating OAM entangled states) and generate Hermite-Gaussian (HG) modes entangled states. 
Zhi-Wei Wang, Xi-Feng Ren, Yun-Feng Huang, Yong-Sheng Zhang and   Guang-Can Guo