Calculating the ground state energy of benzene under spatial deformations with noisy quantum computing.

In this manuscript, we calculate the ground state energy of benzene under spatial deformations by using the variational quantum eigensolver (VQE). The ultimate goal of the study is estimating the feasibility of using quantum computing ansatze on near-term devices for solving problems with large number of orbitals in regions where classical methods are known to fail. The center of our study are the hardware efficient and quantum unitary coupled cluster ansatz (qUCC). Our advanced simulation platform allows us to incorporate a realistic idle noise model - describing noise in quantum devices with a full Krauss operator formalism. We find that the hardware efficient ansatz in the presence of realistic noise outperforms mean field-methods and full-configuration interaction with orbital freezing for extreme deformations of benzene. On the other hand the qUCC ansatz has deeper circuits and thus the effect of noise is so extreme that the energies obtained with that method do not outperform mean-field theories. We therefore foresee that the qUCC method will remain a method for simulators of quantum computers in the pre-error-correction era, while the hardware efficient ansatz can be utilized on current day hardware.