APATCC-10 PROGRAM

Correlated reference assisted quantum computing solver

Lan Nguyen Tran

International University, Vietnam National University - HCM

We propose an active-space approximation to reduce the quantum resources required for variational quantum eigensolver (VQE). Starting from the unitary coupled-cluster (UCC) ansatz, we divide the total excitation operator into internal and external contributions according to the active-inactive partitioning of the orbital space. The inactive space is treated using a correlated mean-field theory called one-body second-order MØller-Plesset perturbation theory (OBMP2), derived using the canonical transformation and the cumulant approximation. Employing the downfolding technique, we arrive at the active-space Hamiltonian solved by VQE composed of the bare Hamiltonian and a potential caused by the internal-external interaction. We have tested our method on different molecules and shown that our approach can dramatically outperform the active-space VQE with uncorrelated Hartree-Fock reference. We also extend our approach to periodic systems, making quantum computing more feasible for materials.