  The factorized form of the unitary coupled cluster ansatz is a popular state
preparation ansatz for electronic structure calculations of molecules on
quantum computers. It often is viewed as an approximation (based on the Trotter
product formula) for the conventional unitary coupled cluster operator. In this
work, we show that the factorized form is quite flexible, allowing one to range
from conventional configuration interaction, to conventional unitary coupled
cluster, to efficient approximations that lie in between these two. The
variational minimization of the energy often allows simpler factorized unitary
coupled cluster approximations to achieve high accuracy, even if they do not
accurately approximate the Trotter product formula. This is similar to how
quantum approximate optimization algorithms can achieve high accuracy with a
small number of levels.
