Optimized Low-Depth Quantum Circuits for Molecular Electronic Structure using a Separable Pair Approximation

We present a classically solvable model that leads to optimized low-depth quantum circuits leveraging separable pair approximations. The obtained circuits are well suited as a baseline circuit for emerging quantum hardware and can, in the long term, provide significantly improved initial states for quantum algorithms. The associated wavefunctions can be represented with linear memory requirement which allows classical optimization of the circuits and naturally defines a minimum benchmark for quantum algorithms. In this work, we employ directly determined pair-natural orbitals within a basis-set-free approach. This leads to an accurate representation of the one- and many-body parts for weakly correlated systems and we explicitly illustrate how the model can be integrated into variational and projective quantum algorithms for stronger correlated systems.