Eigenstates of linear combinations of two boson creation and   annihilation operators : An algebraic approach
  Eigenstates of the linear combinations $a^2+\beta a^{\dagger2}$ and $ab+\beta a^\dagger b^\dagger$ of two boson creation and annihilation operators are presented. The algebraic procedure given here is based on the work of Shanta et al. [Phys. Rev. Lett. {\bf 72}, 1447, 1994] for constructing eigenstates of generalized annihilation operators. 
P. Shanta, S. Chaturvedi and V.Srinivasan