Symmetry-adapted factorized unitary coupled cluster ansatz for quantum computer

For variational quantum eigensolver (VQE) algorithm exploitation of Hamiltonian symmetry enables us to search through a limited size of the Hilbert space and reach correct eigenstate protected by symmetry. We will use unitary coupled cluster as a state preparation ansatz for VQE, where cluster operators will be adapted to a particular spin symmetry. Furthermore, each spin-adapted operators will be factorized using the Cartan decomposition to get an ansatz which can be easily utilized within a quantum algorithm. We will apply this method to various low lying states of open-shell molecules, where non spin-adapted ansatz will face trouble to converge to a correct eigenstate.